Correct review suggestions and manual update

Author: peternewell

Source/Documentation/Manual/sound.rst

@@ -433,7 +433,7 @@ ORTS
 ^^^^
 
 The sound objects attached to a vehicle (wagon or loco) can respond in volume and frequency to changes in the vehicle's properties.
-There are 7 properties:
+There are a number of triggers as follows:
 
 - distance squared from a sound source (m\ :sup:`2`)
 
@@ -445,9 +445,11 @@ There are 7 properties:
 
 - 3 variables in range 0 - 1:
 
-  - Variable1 reflects the throttle
+  - Variable1 reflects the throttle. For steam locomotives it is possible to have multiple steam engines, thus this variable can be applied
+   to each engine, by using a sound trigger of the form ``Variable1_x_inc_past`` or ``Variable1_x_dec_past``, where x = steam engine number.
 
-  - Variable2 reflects the engine's RPM (diesel) or Tractive Force (electric) or cylinder pressure (steam)
+  - Variable2 reflects the engine's RPM (diesel) or Tractive Force (electric) or cylinder pressure (steam). Where a Booster Engine is fitted, 
+  then ``Variable2BoosterControlled`` can be used to control cylinder pressure for booster engines on steam locomotives.
 
   - Variable3 reflects the dynamic brake (diesel | electric) or fuel rate (steam)
 

Source/Orts.Simulation/Simulation/RollingStocks/MSTSLocomotive.cs

@@ -2456,7 +2456,7 @@ protected virtual void UpdateAxleDriveForce()
         /// <summary>
         /// This function applies a sign to the motive force as a function of the direction of the train.
         /// </summary>
-        protected virtual void ApplyDirectionToTractiveForce(ref float tractiveForceN, int numberofengine )
+        protected virtual void ApplyDirectionToTractiveForce(ref float tractiveForceN, int numberofengine = 0 )
         {
             if (Train.IsPlayerDriven)
             {

Source/Orts.Simulation/Simulation/RollingStocks/MSTSSteamLocomotive.cs

@@ -844,6 +844,17 @@ private bool ZeroError(float val1, float val2, string name)
             return true;
         }
 
+        private bool ZeroError(float val1, string name)
+        {
+            if (val1 > 0)
+                return false;
+            if (Simulator.Settings.VerboseConfigurationMessages)
+            {
+                Trace.TraceWarning("Steam engine value {1} must be defined and greater than zero in {0}", WagFilePath, name);
+            }
+            return true;
+        }
+
         /// <summary>
         /// Parse the wag file parameters required for the simulator and viewer classes
         /// </summary>
@@ -1191,9 +1202,9 @@ public override void Initialize()
                 MSTSCylinderStrokeM = 1;
             if (ZeroError(DriverWheelRadiusM, SteamEngines[0].AttachedAxle.WheelRadiusM, "MSTSWheelRadius"))
                 DriverWheelRadiusM = Me.FromIn(30.0f); // Wheel radius of loco drive wheels can be anywhere from about 10" to 40"
-            if (ZeroError(MaxBoilerPressurePSI, 1, "MaxBoilerPressure"))
+            if (ZeroError(MaxBoilerPressurePSI, "MaxBoilerPressure"))
                 MaxBoilerPressurePSI = 1;
-            if (ZeroError(BoilerVolumeFT3, 1, "BoilerVolume"))
+            if (ZeroError(BoilerVolumeFT3, "BoilerVolume"))
                 BoilerVolumeFT3 = 1;
 
             // For light locomotives reduce the weight of the various connecting rods, as the default values are for larger locomotives. This will reduce slip on small locomotives

Source/RunActivity/Viewer3D/Popups/HUDWindow.cs

@@ -585,7 +585,7 @@ void TextPageConsistInfo(TableData table)
         }
 
         /// <summary>
-        /// Calculates Whyte noatation for the vehicle
+        /// Calculates Whyte notation for the vehicle
         /// For duplex steam locomotives wheel axles can be grouped under the main object shape, and hence the multiple engines will be counted as a single grouping.
         /// For multiple engines, the number of wheels defined in the attached axles will be used to determine the axles in the "non-bogie" groupings.
         /// </summary>