diff --git a/Documentation/user-manual.txt b/Documentation/user-manual.txt
index cb77a0586..773524600 100644
--- a/Documentation/user-manual.txt
+++ b/Documentation/user-manual.txt
@@ -1683,7 +1683,7 @@ CCR equipment provide actual measurements of pO~2~, derived from oxygen sensors.
 In this case the graph for oxygen partial pressure
 should be fairly flat, reflecting the setpoint settings during the dive. The mean
 pO~2~ is NOT the mean oxygen partial pressure as given by the CCR equipment, but
-a value xalculated by _Subsurface_ as follows:
+a value calculated by _Subsurface_ as follows:
 
 - For TWO O~2~ sensors the mean value of the two sensors are given.
 
@@ -1691,6 +1691,8 @@ a value xalculated by _Subsurface_ as follows:
   differences of more than 0,1 bar in the simultaneous readings of different sensors are
   treated as spurious. If one of the three sensors provides spurious data, it is ignored.
 
+- If no sensor data is available, the pO~2~ value is assumed to be equal to the setpoint.
+
 The mean pO~2~ of the sensors is indicated with a green line,
 
 The oxygen setpoint values as well as the readings from the individual
@@ -2629,10 +2631,13 @@ This panel allows two type of selections:
 
  ** _Default CCR setpoint for dive planning:_ Specify the O~2~ setpoint for a
     CCR dive plan. This determines the pO~2~ that will be maintained
-    during a particular dive.
+    during a particular dive. This is the setpoint that is used at the start
+    of any CCR dive. Setpoint changes during the dive can be added via the
+    profile context menu.
 
  ** _pSCR O~2~ metabolism rate:_ For a semiclosed rebreather (pSCR) system, this is the
-    volume of oxygen used by a diver each minute. Set this value for pSCR dive planning.
+    volume of oxygen used by a diver each minute. Set this value for pSCR dive planning
+    and decompression calculations.
 
  ** _pSCR ratio:_ For pSCR equipment the dump ratio is the ratio of gas released to the
     environment to that of the gas recirculated to the diver. Set this value for a
@@ -2857,6 +2862,25 @@ level is indicated in the _Dive Plan Details_. This duration INCLUDES the transi
 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.
 
+=== Planning rebreather dives
+
+To plan a dive using a passive semi-closed rebreather (pSCR), select "pSCR" rather than
+"Open circuit" in the Planning tab. This takes the oxygen drop in the rebreather into account.
+The parameters of the pSCR can be set in the preferences in the Graph tab. A warning apears
+in the dive plan details, if the pO~2~ drops below what is considered a save value. For pSCR dives,
+the gas consumption calculation takes into account the pSCR ratio (default 10:1).
+
+To plan a dive using a closed circuit rebreather (CCR), select the "CCR" option in the PLannig tab.
+This makes all user entered segments use the default setpoint value (configured in the Preferences
+in the Graph tab). The gases from the gas list are considered to be diluent gases (the oxygen tank is
+implicitely assumed to be present).
+
+Then, individual setpoints can be set for dive segments in the "Dive planner points" table. A zero setpoint
+means the diver bails out to open circuit mode for that segment. The decompression is always calculated
+with the setpoint of the last manually entered segment. So, to plan an bail out ascent for a
+CCR dive, add a one minute dive segment in the end with a setpoint value of 0. The decompresseion
+algorithm does not switch decogases automatically in CCR mode (but of course for bail out ascents).
+
 [[S_Replan]]
 === Modifying an existing dive plan