diff --git a/examples/MVLinac/MLC.txt b/examples/MVLinac/MLC.txt
index 439b7cf..f41c06a 100644
--- a/examples/MVLinac/MLC.txt
+++ b/examples/MVLinac/MLC.txt
@@ -2,15 +2,18 @@
 # Reference for geometry: Jabbari et al, J Med Signal Sens 3(3):172-179
 
 ########################### Key Parameters In MLC.txt ################################
+# The parameters in MLC.txt are intended as defaults to be adjusted in higher level
+# parameter control files FullTxHead.txt or Field.txt
+#
 # Parameters available for adjustment...
 # SourceToUpstreamSurfaceDistance: Distance from x-ray target to MLC
-# LeafTravelAxis: Direction of jaw travel, either along IEC_B Xb or Yb
+# MLC/RotZ: MLC orientation, dependent on direction of leaf travel along IEC_B
 # MaximumLeafOpen: Maximum distance permitted for leaf to open on either side of Zb
 # Thickness: Thickness of the MLC leaves in Zb
 # Length: Length of the MLC leaves in direction of travel
 # LeafWidths: Vector of leaf widths, same sequence of leaf widths on each MLC bank     
-# NegativeFieldSetting: NegativeFieldSetting <= PositiveFieldSetting for opposing leaves
-# PositiveFieldSetting: Positive leaf positions projected to isocenter 
+# NegativeFieldSetting: Negative leaf positions (IEC X1) projected to isocenter <= PositiveFieldSetting
+# PositiveFieldSetting: Positive leaf positions (IEC X2) projected to isocenter >= NegativeFieldSetting
 #
 # Parameters calculated from other parameters...
 # SAD: Source to axis distance (isocenter coincides with gantry co-ordinates origin) 
@@ -32,14 +35,16 @@ d:Ge/MLC/DistSourceToSAD = Ge/MLC/SAD - Ge/MLC/SourceToUpstreamSurfaceDistance c
 d:Ge/MLC/HalfThickness = 0.5 * Ge/MLC/Thickness cm
 d:Ge/MLC/TransZ = Ge/MLC/DistSourceToSAD - Ge/MLC/HalfThickness cm
 
-d:Ge/MLC/LeafTravelAxisX = 0. deg # Constant to help remember angle for X Axis Travel
-d:Ge/MLC/LeafTravelAxisY = 90. deg # Constant to help remember angle for Y Axis Travel
-d:Ge/MLC/RotZ = Ge/MLC/LeafTravelAxisX deg # Set to one of the above two constants
-
-# MLC leaf widths and positions, projected to isocenter for 10 cm x 20 cm field
+# MLC orientation, leaf widths and positions, projected to isocenter
+# Default 20 cm wide, 50 cm long field at plane of isocenter (at SAD) with all leaves open
+d:Ge/MLC/MLCRotZforTravelAlongIECX = 0. deg # Constant for leaf travel along IEC X axis – DO NOT CHANGE
+d:Ge/MLC/MLCRotZforTravelAlongIECY = -90. deg # Constant for leaf travel along IEC Y axis – DO NOT CHANGE
+d:Ge/MLC/RotZ = Ge/MLC/MLCRotZforTravelAlongIECY deg # Set to one of the above two constants
+# MLC orientation, leaf widths and positions, projected to isocenter for 20 cm x 50 cm field
+# IEC leaf number depends on direction of leaf motion: For Xb leaf 1 is first, Yb leaf 1 is last
 dv:Ge/MLC/LeafWidths           = 42 5. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 5. cm
-dv:Ge/MLC/NegativeFieldSetting = 42 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. -5. -5. -5. -5. -5. -5. -5. -5. -5. -5. -5. -5. -5. -5. -5. -5. -5. -5. -5. -5. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. cm
-dv:Ge/MLC/PositiveFieldSetting = 42 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. cm
+dv:Ge/MLC/NegativeFieldSetting = 42 -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. -10. cm
+dv:Ge/MLC/PositiveFieldSetting = 42 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. 10. cm
 
 s:Ge/MLC/DrawingStyle     = "Solid"
 b:Ge/MLC/PrintInformation = "True"