The Dive Profile (a graphical representation of the depth of the dive as a function of time) is shown in the panel on the top right hand of the Subsurface window. When a dive is manually added to a logbook, Subsurface presents a default dive profile that needs to be modified to best represent the dive described:

Modifying the dive profile: When the cursor is moved around the dive profile, its position is shown by two right-angled red lines as seen below. The time and depth represented by the cursor are indicated at the top of the black information box (@ and D). The units (metric/imperial) on the axes are determined by the Preference settings. The dive profile itself comprises several line segments demarcated by waypoints (white dots on the profile, as shown above). The default dive depth is 15 m. If the dive depth was 20 m then you need to drag the appropriate waypoints downward to 20 m. To add a waypoint, double-click on any line segment. To move an additional waypoint, drag it. To remove a waypoint, right-click on it and choose "Remove this point" from the context menu. Drag the waypoints to represent an accurate time duration for the dive. Below is a dive profile for a dive to 20 m for 30 min, followed by a 5 minute safety stop at 5 m.

Specifying the gas composition: The gas composition used is indicated along the line segments of the dive profile. This defaults to the first gas mixture specified in the Equipment tab, which was air in the case of the profile above. The gas mixtures of segments of the dive profile can be changed by right-clicking on the particular waypoint and selecting the appropriate gas from the context menu. Changing the gas for a waypoint affects the gas shown in the segment to the left of that waypoint. Note that only the gases defined in the Equipment tab appear in the context menu (see image below).

With the profile now defined, more details must be added to have a fuller record of the dive. To do this, the Notes and the Equipment tabs on the top left hand of the Subsurface window should be used. Click on this link for instructions on how to use these tabs.

The use of dive computers allows the collection of a large amount of information about each dive, e.g. a detailed record of depth, duration, rates of ascent/descent and of gas partial pressures. Subsurface can capture this information, using dive details from a wide range of dive computers. The latest list of supported dive computers can be found at: Supported dive computers.

To import dive information from a dive computer to a computer with Subsurface, the two pieces of equipment must communicate with one another. This involves setting up the communications port (or mount point) of the computer with Subsurface that communicates with the dive computer. To set up this communication, users need to find the appropriate information to instruct Subsurface where and how to import the dive information. Appendix A provides the technical information to help the user achieve this for different operating systems and Appendix B has dive computer specific information.

After this, the dive computer can be hooked up to the user’s PC using these steps:

Dive computers tend to keep a certain number of dives in memory, even though these dives have already been imported to Subsurface. For that reason, if the dive computer allows this, Subsurface only imports dives that have not been uploaded before. This makes the download process faster on most dive computers and also saves battery power of the dive computer (at least for those not charging while connected via USB).

Bluetooth is becoming a more common way of communication between dive computers and Subsurface, for or instance, the Shearwater Petrel Mk2 and the OSTC Mk3. Subsurface provides a largely operating system independent Bluetooth interface. Setting up Subsurface for Bluetooth communication requires four steps:

Select the Download dialogue by selecting Import → Import from dive computer from the Main Menu. After checking the box labelled "Choose Bluetooth download mode", the dialogue below appears.

It may be necessary to distinguish between different dive computers used to upload dive logs to Subsurface. For instance if a buddy’s dive computer is the same make and model as your own and dive logs are uploaded from both dive computers to the same Subsurface computer, then you might like to call one "Alice’s Suunto D4" and the other "Bob’s Suunto D4". Alternatively, consider a technical diver who dives with two or more dive computers of the same model, the logs of both (or all) being uploaded. In this case it might be prudent to call one of them "Suunto D4 (1)" and another "Suunto D4 (2)". This is easily done in Subsurface. On the Main Menu, select Log → Edit device names. A dialog box opens, showing the current Model, ID and Nickname of the dive computers used for upload. Edit the Nickname field for the appropriate dive computer. After saving the Nickname, the dive logs show the nickname for that particular device instead of the model name, allowing easy identification of devices.

With the uploaded dives in the Dive List, the information from the dive computer is not complete and more details must be added to have a full record of the dives. To do this, the Notes and the Equipment tabs on the top left hand of the Subsurface window should be used.

METHOD 1: After uploading dives from a dive computer, the dive profiles of each is shown in the Dive profile tab, as well as a few items of information in the Notes tab (e.g. water temperature) and in the Equipment tab (e.g. gas pressures and gas composition). Other fields remain empty. It may be useful to simultaneously edit some of the fields in the Notes and Equipment tabs. For instance, it’s possible that a diver performed several dives during a single day, using identical equipment at the same dive site, or with the same divemaster and/or buddy or tags. Instead of completing the information for each dive separately, select all the dives for that day in the Dive List and insert the same information in the Notes and Equipment fields that need identical information. This is done by editing the dive notes or the equipment for any one of the selected dives.

Simultaneous editing only works with fields that do not already contain information. This means if some fields have been edited for a particular dive among the selected dives, these are not changed while editing the dives simultaneously. Technically, the rule for editing several dives simultaneously is: if the data field being edited contains exactly the same information for all the dives that have been selected, the new, edited information is substituted for all the selected dives. Otherwise only the edited dive is changed, even though several dives have been selected in the Dive List. This speeds up the completion of the dive log after several similar dives.

METHOD 2:There is a different way of achieving the same goal. Select a dive with all the appropriate information typed into the Notes and Equipment tabs. Then, from the main menu, select Log → Copy dive components. A box is presented with a selection of check boxes for most of the fields in the Notes and Equipment tabs. Select the fields to be copied from the currently selected dive, then select OK. Now, in the Dive List, select the dives into which this information is to be pasted. Then, from the main menu, select Log → Paste dive components. All the selected dives now contain the data initially selected in the original source dive log.

Many divers wish to annotate dives with text that indicate particular events, e.g. "Saw dolphins", or "Released surface buoy". This is easily done:

The information entered in the Notes tab and the Equipment tab can be saved by using the two buttons on the top right hand of the Notes tab. If the Apply changes button is clicked, the dive data are saved in the memory image of the dive. If the Discard changes button is clicked, the newly entered dive data are erased from the computer memory, although the dive profile is retained. When the user exits Subsurface there is a final prompt to confirm the new data should now be saved permanently on the computer disk.

Importing dives from other software is done through a universal interface activated by selecting Import from the Main Menu, then clicking on Import Log Files. This brings up dialogue A, below.

Towards the bottom right is a dropdown selector with a default label of Dive Log Files which accesses different types of direct imports available, as in dialogue B, above. Currently these are:

Selecting the appropriate format and then the specific log file in the large window containing the file list on the right of the dialogue, opens the imported dive log in the Subsurface Dive List. Some other formats not accessible through the Import dialogue are also supported, as explained below.

OSTC Tools is a Microsoft-based suite of dive download and dive management tools for the OSTC family of dive computers. OSTC Tools downloads dive data from the dive computer and stores it as a binary file with file extension .dive . Subsurface can directly import these files when using the universal import dialogue. From the dropdown list at the bottom right select OSTCTools Files (.dive .DIVE). This makes the OSTC Tools dive logs visible in the file list panel. Select one or more dive, then click the Open button. The OSTC dives are shown in the Dive List panel.

All H&W devices supported by OSTCTools can be imported to Subsurface. This includes OSTC, OSTC Mk2, OSTC 2N/2C, OSTC3, OSTC Sport, and probably although untested, Frog, OSTC2 and OSTC CR.

Please remember that OSTCTools is not true diving log software, but rather a useful set of tools for analysis and management of OSTC devices. Only raw dive computer data will be imported to Subsurface; the rest of the data (buddies, equipment, notes, etc) need to be completed manually.

Since Mares uses proprietary Windows software not compatible with multi-platform applications, these dive logs cannot be directly imported into Subsurface. Mares dive logs need to be imported using a three-step process, using www.divelogs.de as a gateway to extract the dive log information.

Importing dive information from divelogs.de is simple, using a single dialogue box. The Import → Import from Divelogs.de option should be selected from the Main Menu. This brings up a dialogue box (see image A below). Enter a user-ID and password for divelogs.de and then select the Download button. Download from divelogs.de starts immediately, displaying a progress bar in the dialogue box. At the end of the download, the success status is shown (see image B, below). The Apply button should then be selected, after which the imported dives appear in the Subsurface Dive List panel.

A comma-separated file (.csv) can be used to import dive information either as dive profiles (as in the case of the APD Inspiration and Evolution closed circuit rebreathers) or as dive metadata (in case the user keeps dive data in a spreadsheet). The CSV format is a universal simplified format that allows easy information exchange between different computers or software packages. For an introduction to CSV-formatted files see A Diver’s Introduction To CSV Files. Subsurface dive logs can also be exported in CSV format to other software that reads this format. See APPENDIX D: Exporting a spreadsheet to CSV format for information that may be helpful for importing spreadsheet-based data into Subsurface.

Using the Subsurface Companion App on an Android device or iPhone with GPS, the coordinates for the diving location can be automatically passed to the Subsurface dive log. The Companion App stores dive locations on a dedicated Internet server. Subsurface can collect the locations from the server. To do this:

Left-lick on a dive or on a group of dives on the dive list, bringing up the Dive list context Menu. Right-click the appropriate option to import images either from file or from the Internet. The system file browser appears. Select the folder and photographs that need to be loaded into Subsurface and click the Open button.

This brings up the time synchronization dialog, shown below. The time synchronization is not perfect between the dive computer used during a dive, and the camera used during that same dive. These two devices often differ by several minutes. Subsurface attempts to synchronize these two devices so that the exact times of photographs can be used to position photographs on the dive profile.

Subsurface synchronizes camera with dive computer in three ways:

If the timestamp of a photograph is more than 30 minutes before or after the dive, it is not placed on the dive profile (see the red warning in the image above). However, If the appropriate checkbox is selected (see image above) these images can still be placed on the Photos tab of the Notes panel so that all photos associated with a dive are visible, including photos taken before or after the dive.

After the images have been loaded, they appear in two places:

This results in a profile display as in the image below:

Hover the mouse over any of the photo stubs. A thumbnail photo is shown of the appropriate photo. See the image below:

Clicking on the thumbnail brings up a full size photo overlaid on the Subsurface window, allowing a good view of the photographs (see the image below). Note that the thumbnail has a small dustbin icon in the bottom right hand corner (see image above). Selecting the dustbin removes the image from the dive. Be careful when clicking on a thumbnail. Images can also be deleted using the Photos tab (see text below).

Photographs associated with a dive are shown as thumbnails in the Photos tab of the Notes panel. Photos taken in rapid succession during a dive (therefore sometimes with large overlap on the dive profile) can easily be accessed in the Photos tab. This tab serves as a tool for individually accessing the photos of a dive, while the stubs on the dive profile show when during a dive a photo was taken. Single-click a thumbnail in the Photos panel to select a photo. Double-click a thumbnail to view the full-sized image, overlaying the Subsurface window. Deleted a photo from the Photos panel by selecting it (single-click) and then by pressing the Del key on the keyboard. This removes the photo BOTH from the Photos tab as well as the dive profile.

Most underwater photographers store photos on an external drive. If such a drive can be mapped by the operating system (almost always the case) the photos can be directly accessed by Subsurface. This eases the interaction between Subsurface and an external repository of photos. When associating a dive profile with photos from an external drive, the normal procedure of selection and synchronization (see text above) is used. After the external drive has been disconnected, Subsurface cannot access these photos any more. If the display of photos is activated (using the toolbox icon to the left of the Dive Profile), the program shows a small white dot where each photo should be on the dive profile. In addition the Photos tab shows only the file names of the photos. If the external drive with the photos is re-connected, the photos can be seen in the normal way.

After a photograph has been loaded into Subsurface and associated with a specific dive, Subsurface saves the directory path where the photo lies as well as the file name of the photo, in order to find it when the dive is opened again. If the photo or the whole photo collection is moved to another drive or to a different machine, the path to the photo changes. Now, Subsurface looks for the photos at their original location before they were moved, cannot find them and cannot display them. Because, after moving photos, large numbers of photos may need to be deleted and re-imported from the new location, Subsurface has a mechanism to ease this inconvenience: automatic updates using fingerprints.

When a photo is loaded into Subsurface, a fingerprint for the image is calculated and stored with the other reference information for that photo. After moving a photo collection (that has already been loaded into Subsurface) to a different directory, disk or computer, Subsurface can:

if there is a match between a calculated fingerprint and the one calculated when a photo was originally loaded into Subsurface (even if the original file name has changed), automatically update the directory information so that Subsurface can find the photo in the new moved directory.

This is done by selecting from the Main Menu: File → Find moved images. This brings up a window within which the NEW directory of the photos needs to be specified. Select the appropriate directory and click the Scan button towards the bottom right of the panel. The process may require several minutes to complete, after which Subsurface will show the appropriate photographs when a particular dive is opened.

Subsurface easily handles dives involving more than one cylinder. Multi-cylinder diving usually happens (a) if a diver doesn’t have enough gas for the complete dive in a single cylinder; (b) if a diver needs more than one gas mixture because of the depth or the decompression needs of the dive. For this reason multi-cylinder dives are often used by technical divers who dive deep or long. As far as Subsurface is concerned, there are only two types of information that need to be provided:

When this is complete, Subsurface indicates the appropriate use of cylinders in the dive profile. Below is a two-cylinder dive, starting off with EAN28, then changing cylinders to EAN50 after 26 minutes for decompression.

Sidemount diving is just another form of multi-cylinder diving, often with both or all cylinders having the same gas mixture. Although it’s a popular configuration for cave divers, sidemount diving can be done by recreational divers who’ve completed the appropriate training. Sidemount dive logging involves three steps, exactly as with multi-cylinder dives above:

To log pSCR dives, no special procedures are required. Use the normal steps outlined above:

If a pSCR Dive Mode has been selected, the dive ceiling for that is adjusted for the oxygen drop across the mouthpiece, which often requires longer decompression periods. Below is a dive profile of a pSCR dive using EAN36 on the back cylinder and oxygen for decompression. Note that this dive lasted over two hours.

The Information box displays a large range of information about the dive profile. Normally the Information Box is located to the top left of the Dive Profile panel. If the mouse points outside of the Dive Profile panel, then only the top line of the Information Box is visible (see left-hand part of figure (A) below). The Information Box can be moved around in the Dive Profile panel by click-dragging it with the mouse so that it is not obstructing important detail. The position of the Information Box is saved and used again during subsequent dive analyses.

When the mouse points inside the Dive Profile panel, the information box expands and shows many data items. In this situation, the data reflect the time point along the dive profile shown by the mouse cursor (see right-hand part of figure (B) above where the Information Box reflects the situation at the position of the cursor [arrow] in that image). Moving the cursor horizontally lets the Information Box show information for any point along the dive profile. It gives extensive statistics about depth, gas and ceiling characteristics of the particular dive. These include: Time period into the dive (indicated by a @), depth, cylinder pressure (P), temperature, ascent/descent rate, surface air consumption (SAC), oxygen partial pressure, maximum operating depth, equivalent air depth (EAD), equivalent narcotic depth (END), equivalent air density depth (EADD), decompression requirements at that instant in time (Deco), time to surface (TTS), the calculated ceiling, as well as of the statistics in the Information Box, shown as four buttons on the left of the profile panel. These are:

Figure (B) above shows an information box with a nearly complete set of data.

The dive profile can include graphs of the partial pressures of O₂, N₂, and He during the dive (see figure above) as well as a calculated and dive computer reported deco ceilings (only visible for deep, long, or repetitive dives). Partial pressures of oxygen are indicated in green, nitrogen in black, and helium in dark red. These partial pressure graphs are shown below the profile data.

The air consumption graph displays the tank pressure and its change during the dive. The air consumption takes depth into account so that even when manually entering the start and end pressures the graph, is not a straight line. Like the depth graph, the slope of the tank pressure provides information about the momentary SAC rate (Surface Air Consumption) when using an air integrated dive computer. Here the color coding is not relative to some absolute values but relative to the mean normalized air consumption during the dive. So areas in red or orange indicate times of increased normalized air consumption while dark green reflects times when the diver was using less gas than average.

It is possible to zoom into the profile graph. This is done either by using the scroll wheel / scroll gesture of the mouse or trackpad. By default Subsurface always shows a profile area large enough for at least 30 minutes and 30m (100ft) – this way short or shallow dives are easily recognizable; something free divers won’t care about.

The profile can also include the dive computer reported ceiling (more precisely, the deepest deco stop that the dive computer calculated for each particular moment in time) as a red overlay on the dive profile. Ascent ceilings occur when a direct ascent to the surface increases the risk of a diver suffering from decompression sickness (DCS) and it is necessary to either ascend slower or to perform decompression stop(s) before ascending to the surface. Not all dive computers record this information and make it available for download; for example none of the Suunto dive computers make these data available to divelog software. Subsurface also calculates ceilings independently, shown as a green overlay on the dive profile. Because of the differences in algorithms used and amount of data available (and other factors taken into consideration at the time of the calculation) it’s unlikely that ceilings from dive computers and from Subsurface are the same, even if the same algorithm and gradient factors (see below) are used. It’s also quite common that Subsurface calculates a ceiling for non-decompression dives when the dive computer stayed in non-deco mode during the whole dive (represented by the dark green section in the profile at the beginning of this section). This is because Subsurface’s calculations describe the deco obligation at each moment during a dive, while dive computers usually take the upcoming ascent into account. During the ascent some excess nitrogen (and possibly helium) are already breathed off so even though the diver technically encountered a ceiling at depth, the dive still does not require a specific deco stop. This feature lets dive computers offer longer non-stop bottom times.

The context menu for the Dive Profile is accessed by right-clicking while the mouse cursor is over the Dive Profile panel. The menu allows creating Bookmarks, Gas Change Event markers, or manual CCR set-point changes other than the ones that might have been imported from a Dive Computer. Markers are placed against the depth profile line, with the time of the event determined by the mouse cursor when the right mouse button was clicked to bring up the menu. Gas Change events involve a selection of which gas is being switched TO. The list of choices is based on the available gases defined in the Equipment Tab. Setpoint change events open a dialog letting you choose the next setpoint value. As in the planner, a setpoint value of zero shows the diver is breathing from an open circuit system while any non-zero value shows the use of a closed circuit rebreather (CCR). By right-clicking while over an existing marker a menu appears, adding options to allow deletion of the marker, or to allow all markers of that type to be hidden. Hidden events can be restored to view by selecting Unhide all events from the context menu.

The default information in the Dive List includes, for each dive, Dive_number, Date, Rating, Dive_depth, Dive_duration and Dive_location. This information can be controlled and changed by right-clicking on the header bar of the Dive List. For instance, a right-click on the Date header brings up a list of items that can be shown in the dive list (see above). Select an item to be included in the Dive List or to be deleted (reflected by the check symbols) and the list is immediately updated. Preferences for information shown in the Dive List are saved and used when Subsurface is re-opened.

Normally, in the dive list, minimal information is included in the trip title. More information about a trip can be added by selecting its trip title bar from the Dive List. This shows a Trip Notes tab in the Notes panel. Here you can add or edit information about the date/time, the trip location and any other general comments about the trip as a whole (e.g. the dive company that was used, the general weather and surface conditions during the trip, etc.). After entering this information, select Save from the buttons at the top right of the Trip Notes tab. The trip title in the Dive List panel should now reflect the edited information.

Once the dives have been grouped into trips, you can expand one or more trips by clicking the expansion button [+/-] on the left of each trip title. This expands the selected trip, revealing individual dives during the trip.

After selecting a particular trip in the dive list, the context menu allows several options to expand or collapse dives within trips. This includes expanding all trips and collapsing all trips.

After selecting a trip title, the context menu allows the merging of trips by either merging the selected trip with the trip below or with the trip above. (Merge trip with trip below; Merge trip with trip above)

If a trip includes ten dives, you can split this trip into two trips (trip 1: top 4 dives; trip 2: bottom 6 dives) by selecting and right-clicking the top four dives. The resulting context menu lets the user create a new trip by choosing the option Create new trip above. The top four dives are then grouped into a separate trip. The figures below show the selection and context menu on the left (A) and the completed action on the right (B):

Dives can be permanently deleted from the dive log by selecting and right-clicking them to bring up the context menu, then selecting Delete dive(s). Typically this would apply to a case where a user wishes to delete workshop calibration dives of the dive computer or dives of extremely short duration.

You can unlink dives from the trip to which they belong. To do this, select and right-click the relevant dives to bring up the context menu. Then select the option Remove dive(s) from trip. The dive(s) now appear immediately above or below the trip to which they belonged, depending on the date and time of the unlinked dive.

Selected dives can be moved from the trip to which they belong and placed within a separate trip. To do this, select and right-click the dive(s) to bring up the context menu, and then select Create new trip above.

Sometimes it’s necessary to adjust the start time of a dive. This may apply to situations where dives are done in different time zones or when the dive computer has a wrong time. To do this, select and right-click the dive(s) to be adjusted. This brings up the context menu on which the Shift times option should be selected. You must then specify the time (in hours and minutes) by which the dives should be adjusted and click on the option of whether the time adjustment should be earlier or later.

Sometimes a dive is briefly interrupted, for example, if a diver returns to the surface for a few minutes, resulting in two or more dives being recorded by the dive computer and appearing as different dives in the Dive List panel. Merge these dives onto a single dive by selecting the appropriate dives, right-clicking them to bring up the context menu and then selecting Merge selected dives. It may be necessary to edit the dive information in the Notes panel to reflect events or conditions that apply to the merged dive. The figure below shows the depth profile of two dives that were merged:

Important actions on dives or trips, described above, can be undone or redone. This includes: delete dives, merge dives, renumber dives and shift dive times. To do this after performing any of these actions, from the Main Menu select Edit. This brings up the possibility to Undo or Redo an action.

Recreational mode is what comes closest to planning a dive based on the non-decompression limit (NDL). It computes the maximum time a diver can stay at the current depth without needing mandatory decompression stops and without using more than the existing gas (minus a reserve). The planner automatically takes into account the nitrogen load incurred in previous dives. But conventional dive tables are also used in a way that can take into account previous dives. Why use a dive planner for recreational dives? Using recreational dive tables, the maximum depth of a dive is taken into account. But few dives are done at a constant depth corresponding to the maximum depth (i.e. a "square" dive profile). This means dive tables overestimate the nitrogen load incurred during previous dives. The Subsurface dive planner calculates nitrogen load according to the real dive profiles of all uploaded previous dives, in a similar way as dive computers calculate nitrogen load during a dive. This means that the diver gets credit, in terms of nitrogen load, for not remaining at maximum depth during previous dives, so a longer subsequent dive can be planned. For the planner to work it’s crucial to upload all previous dives onto Subsurface before doing dive planning. To plan a dive, the appropriate settings need to be defined.

Ensure the date and time is set to that of the intended dive. This allows calculation of the nitrogen load incurred during previous dives.

The dive profile in the planner shows the maximum dive time within no-deco limits using the Bühlmann ZH-L16 algorithm and the gas and depth settings specified as described above. The Subsurface planner allows rapid assessment of dive duration as a function of dive depth, given the nitrogen load incurred during previous dives. The dive plan includes estimates of the amount of air/gas used, depending on the cylinder settings specified under Available gases. If the initial cylinder pressure is set to 0, the dive duration shown is the true no-deco limit (NDL) without taking into account gas used during the dive. If the surface above the dive profile is RED it means that recreational dive limits are exceeded and either the dive duration or the dive depth needs to be reduced.

Below is an image of a dive plan for a recreational dive at 30 meters. Although the no-deco limit (NDL) is 23 minutes, the duration of the dive is limited by the amount of air in the cylinder. That is shown in the text box at the bottom right of the panel, requiring sufficient air for buddy-sharing during ascent.

Non-recreational dive planning involves exceeding the no-deco limits and/or using multiple breathing gases. These dives are planned in three stages:

a) Nitrogen management: This is done by specifying the rates for descent and ascent, as well as the deco model (GFLow, GFHigh or Conservatism level) under the headings Rates and Planning to the bottom left of the planning screen. Two deco models are supported the Bühlmann model and the VPM-B model. Select one of the two models. When selecting the Bühlmann model, the gradient factors (GFhigh and GFlow need to be specified. Initially, the GFHigh and GFLow values in the Preferences panel of Subsurface is used. If these are changed within the planner (see Gas Options within the planner), the new values are used without changing the original values in the Preferences. Gradient Factor settings strongly affect the calculated ceilings and their depths. A very low GFLow value brings on decompression stops early during the dive. ** For more information about Gradient factors, see the section on Gradient Factor Preference settings.

If the VPM-B model is selected, the Conservatism_level needs to be specified on a scale of 0 (least conservative) to 4 (most conservative). This model tends to give deco stops at deeper levels than the Bühlmann model and often results in slightly shorter dive durations than the Bühlmann model, albeit at the cost of higher tissue compartment pressures in the slow tissues. When selecting one of these models, keep in mind they are NOT exact physiological models but only mathematical models that appear to work in practice.

For more information external to this manual see:

The ascent rate is critical for nitrogen off-gassing at the end of the dive and is specified for several depth ranges, using the mean depth as a yardstick. The mean depth of the dive plan is shown by a light grey line on the dive profile. Ascent rates at deeper levels are often in the range of 8-12 m/min, while ascent rates near the surface are often in the range of 4-9 m/min. The descent rate is also specified. If the option Drop to first depth is activated, the descent phase of the planned dive will be at the maximal descent rate specified in the Rates section of the dive setup.

b) Oxygen management: In the Gas Options part of the dive specification, the maximum partial pressure for oxygen needs to be specified for the bottom part of the dive (bottom po2) as well as for the decompression part of the dive (deco po2). Commonly used values are 1.4 bar for the bottom part of the dive and 1.6 bar for any decompression stages. Normally, a partial pressure of 1.6 bar is not exceeded. PO2 settings and the depth at which switching to a gas takes place can also be edited in the Available Gases dialog. Normally the planner decides on switching to a new gas when, during ascent, the partial pressure of the new gas has decreased to 1.6 bar.

c) Gas management: With open-circuit dives this is a primary consideration. Divers need to keep within the limits of the amount of gas within the dive cylinder(s), allowing for an appropriate margin for a safe return to the surface, possibly sharing with a buddy. Under the Gas Options heading, specify the best (but conservative) estimate of your surface-equivalent air consumption (SAC, also termed RMV) in liters/min (for the time being, only SI units are supported). Specify the SAC during the bottom part of the dive (bottom SAC) as well as during the decompression or safety stops of the dive (deco SAC). Values of 15-30 l/min are common. For good gas management, a guess is not sufficient and you needs to monitor gas consumption on a regular basis, dependent on different dive conditions and/or equipment. The planner calculates the total volume of gas used during the dive and issues a warning if you exceeds the total amount of gas available. Good practice demands that divers not dive to the limit of the gas supply but that an appropriate reserve is kept for unforeseen circumstances. For technical diving, this reserve can be up to 66% of the total available gas.

Now you can start the detailed time-depth planning of the dive. Subsurface offers an unique graphical interface for doing planning. The mechanics are similar to hand-entering a dive profile in the dive log part of Subsurface. Upon activating the planner, a default dive of depth 15 m for 20 min is offered in the blue design surface to the top right hand of the screen. The white dots (waypoints) on the profile can be dragged with a mouse. Create more waypoints by double-clicking on the profile line and ensuring the profile reflects the intended dive. Drag the waypoints to represent the depth and duration of the dive. It is NOT necessary to specify the ascent part of the dive since the planner calculates this, based on the existing settings. If any of the management limits (for nitrogen, oxygen or gas) are exceeded, the surface above the dive profile changes from BLUE to RED.

Each waypoint on the dive profile creates a Dive Planner Point in the table on the left of the dive planner panel. Ensure the Used Gas value in each row of that table corresponds to one of the gas mixtures specified in the Available Gases table. Add new waypoints until the main features of the dive have been completed, e.g. the bottom time segment and deep stops (if these are implemented). Leave the remaining waypoints on the ascent to Subsurface. In most cases Subsurface computes additional way points in order to fulfill decompression requirements for that dive. A waypoint can be moved by selecting it and by using the arrow keys. The waypoints listed in the Dive Planner Points dialogue can be edited by hand in order to get a precise presentation of the dive plan. In fact, it is sometimes more easy to create the whole dive profile by editing the Dive Planner Points dialog.

Show any changes in gas cylinder used by indicating gas changes as explained in the section hand-creating a dive profile. These changes should reflect the cylinders and gas compositions defined in the table with Available Gases. If two or more gases are used, automatic gas switches will be suggested during the ascent to the surface. These changes can be deleted by right-clicking the gas change and manually creating a gas change by right-clicking on the appropriate waypoint.

A non-zero value in the "CC set point" column of the table of dive planner points indicates a valid setpoint for oxygen partial pressure and that the segment is dived using a closed circuit rebreather (CCR). If the last manually entered segment is a CCR segment, the decompression phase is computed assuming the diver uses a CCR with the specified set-point. If the last segment (however short) is on open circuit (OC, indicated by a zero set-point) the decompression is computed in OC mode and the planner only considers gas changes in OC mode.

Below is an example of a dive plan to 45m using EAN26, followed by an ascent using EAN50 and using the settings as described above.

Once the above steps have been completed, save by clicking the Save button towards the top middle of the planner. The saved dive plan will appear in the Dive List panel of Subsurface.

The dive plan details

On the bottom right of the dive planner, under Dive Plan Details, the exact details of the dive plan are provided. These details may be modified by checking any of the options under the Notes section of the dive planner, immediately to the left of the Dive Plan Details. If a Verbatim dive plan is requested, a detailed sentence-level explanation of the dive plan is given. If any of the management specifications have been exceeded during the planning, a warning message is printed underneath the dive plan information.

If the option Display segment duration is checked, then the duration of each depth level is indicated in the Dive Plan Details. This duration INCLUDES the transition time to get to that level. However, if the Display transition in deco option is checked, the transitions are shown separately from the segment durations at a particular level.

Bluetooth is most likely already enabled. For pairing with the dive computer choose Control Panel → Bluetooth Devices → Add Wireless Device. This should bring up a dialog showing your dive computer (which should be in Bluetooth mode) and allowing pairing. Right click on it and choose Properties→ COM Ports to identify the port used for your dive computer. If there are several ports listed, use the one saying "Outgoing" instead of "Incoming".

For downloading to Subsurface, the Subsurface drop-down list should contain this COM port already. If not, enter it manually.

Note: If there are issues afterwards when downloading from the dive computer using other software, remove the existing pairing with the dive computer.

Click on the Bluetooth symbol in the menu bar and select Set up Bluetooth Device…. The dive computer should then show up in the list of devices. Select it and go through the pairing process. This step should only be needed once for initial setup.

Once the pairing is complete, the correct device is shown in the Device or Mount Point drop-down in the Subsurface Import dialog.

Be sure Bluetooth is enabled on the Subsurface computer. On most common distributions this should be true out of the box and pairing should be straightforward. For instance, Gnome3 shows a Bluetooth icon on the right of the toolbar at the top of the screen. Users have reported difficulties with some Bluetooth controllers. If you have an onboard controller, try that first. It is simplest if you remove any USB Bluetooth dongles. If you have a USB dongle that came with your dive computer, try that before any others.

Setting up a connection to download dives from your Bluetooth-enabled device, such as the Shearwater Petrel, is not yet an automated process and will generally require the command prompt. It is essentially a three step process.

Ensure the dive computer is in upload mode. On the Shearwater Petrel, Petrel 2 and Nerd cycle through the menu, select Dive Log, then Upload Log. The display will read Initializing, then Wait PC 3:00 and will countdown. Once the connection is established, the display reads Wait CMD … and the countdown continues. When downloading the dive from Subsurface, the display reads Sending then Sent Dive.

To establish the connection, establish root access through sudo or su. The correct permission is required to download the dives in the computer. On most Linux systems this means becoming a member of the dialout group (This is identical as for many dive computers using a Linux USB port, described in the previous section). On the command terminal, enter:

sudo usermod -a -G dialout username

Then log out and log in for the change to take effect.