Documentation: multiple small corrections and improvements

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

Documentation/user-manual.txt

@@ -26,12 +26,16 @@ Subsurface is an open source divelog program that runs on Windows, Mac
 and Linux.
 
 With Subsurface the user can download dive information directly from a
-large number of supported dive computers. Subsurface is able to track
+large number of supported dive computers. Alternatively dives can be
-single- and multi-tank dives using air, Nitrox or TriMix. It displays
+imported from a number of other divelog programs of web
-a dive profile with all related information including air consumption
+services. Dives can also be manually entered.
-and alarms. It also allows logging of information like weights and
+
-exposure protection used, dive masters and dive buddies and enables
+Subsurface is able to track single- and multi-tank dives using air,
-the user to rate dives and provide additional dive notes.
+Nitrox or TriMix. It displays a dive profile with all related
+information including air consumption and alarms. It also allows
+logging of information like weights and exposure protection used, dive
+masters and dive buddies and enables the user to rate dives and
+provide additional dive notes.
 
 With Subsurface the user can track dive locations including GPS
 coordinates (which can also be conveniently entered using a map
@@ -46,7 +50,7 @@ in more than a dozen languages and well supported by an active
 developer community.
 
 While the list of supported dive computers is very long, in this
-manual the Suunto Vyper will be used for all examples.
+manual the Suunto Vyper will be used for most examples.
 
 
 [[S_Requirements]]
@@ -115,7 +119,9 @@ 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. Similarly to the depth graph the tank pressure
-gives you information of the SAC rate when using air integrated dive
+gives you information about the momentary SAC rate (Surface Air
+Consumtion - often also called RMV - Respiratory Minute Volume) when
+using an air integrated dive
 computer. Here the color coding is not relative to some absolute
 values but relative to the average normalized air consumption during
 the dive. So areas that are red or orange indicate times of increased
@@ -127,22 +133,27 @@ tank pressure readings during the dive are available.
 Water temperature is displayed with its own blue line with degree
 markings placed adjacent to significant changes.
 
-It is also possible to zoom in the profile graph. This is done either
+It is possible to zoom into the profile graph. This is done either
 by using the scroll wheel / scroll gesture of your mouse or trackpad
 or by holding down the left mouse button; the zoom area can be changed
 by moving the mouse around the profile. There is also a toggle zoom
 under the 'Log' menu that changes the scale of the dive to fill the
-whole area, useful especially for free divers.
+whole area, useful especially for free divers. 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 intuitively
+recognizable; something that free divers clearly won't care about.
 
 [[S_TecDiveProfile]]
 Tec Information in Dive Profile
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-The dive profile can include Tec settings. Enabling these is described
+The dive profile can include further information that is typically
+more interesting for tec divers. Enabling these is described
 in chapter <<S_SettingUpPreferences,Setting up
 Preferences>>. Basically you can include graphs of the partial
-pressures O2, N2, and He during the dive as well as a calculated deco
+pressures O2, N2, and He during the dive as well as a calculated
-ceiling (only visible for deep, long, or repetitive dives).
+and dive computer reported deco ceilings (only visible for deep,
+long, or repetitive dives).
 
 The partial pressure graphs are added below the profile data, the
 calculated ceiling is shown as a green overlay on top of the dive
@@ -737,15 +748,15 @@ You can set the following options with 'Units':
 |===============================================================================
 | Field        | Units to be displayed
 | Depth        | Your diving depth in Meters or Feet
-| Pressure     | The pressure of your tank(s) in Bar/Ato or PSI (Pressure Square Inch)
+| Pressure     | The pressure of your tank(s) in Bar/Ato or PSI (Pounds per Square Inch)
-| Volume       | The volume of your tank(s) in Liter or CuFt (Cubic Feet) (At sea-level pressure)
+| Volume       | The volume of your tank(s) in Liter (at sea level) or CuFt (Cubic Feet) (at working pressure)
-| Temperature  | The temperature of the water in Celsius or Fahrenheit
+| Temperature  | The temperature of the water in degrees Celsius or Fahrenheit
 | Weight       | The weight of your weight system in kg or lbs
 |===============================================================================
 
 As mentioned earlier when discussing the information visible in the
-dive list at the bottom of the main Subsurface window, you can you can
+dive list at the bottom of the main Subsurface window, you can
-enable/disable some of the colums that can be shown there:
+enable or disable some of the colums that can be shown there:
 
 [width="90%",cols="<33%,67%",options="header"]
 |===============================================================================