diff --git a/base_classes/NXdisk_chopper.nxdl.xml b/base_classes/NXdisk_chopper.nxdl.xml
index 8d040bdf6c..10a1f68f52 100644
--- a/base_classes/NXdisk_chopper.nxdl.xml
+++ b/base_classes/NXdisk_chopper.nxdl.xml
@@ -45,9 +45,23 @@
 		We refer to this below as the "top-dead-center signal".
 
 		Angles and positive rotation speeds are measured in an anticlockwise
-		direction when facing away from the source.
+		direction when facing away from the source unless otherwise specified in the `handedness` field.
 	</doc>
 
+	<field name="handedness">
+		<doc>
+      Direction of measurement for rotation and positions in the disk-chopper.
+      Left is the default for historical reasons and implies positive rotation and angles in an anticlockwise
+      direciton when facing away from the source.
+      Right matches the default NeXus coordinate system and implies positive rotation and angles in an anticlockwise
+      direction when looking towards the source - positive rotation matches the positive roll of the system.
+      Only one from the enumerated list (match text exactly).
+    </doc>
+		<enumeration>
+			<item value="Left" />
+			<item value="Right" />
+		</enumeration>
+	</field>
 	<field name="type">
 		<doc>Type of the disk-chopper: only one from the enumerated list (match text exactly)</doc>
 		<enumeration>
@@ -58,8 +72,7 @@
 	</field>
 	<field name="rotation_speed" type="NX_FLOAT" units="NX_FREQUENCY">
 		<doc>
-			Chopper rotation speed. Positive for anticlockwise rotation when
-			facing away from the source, negative otherwise.
+			Chopper rotation speed.
 		</doc>
 	</field>
 	<field name="slits" type="NX_INT">
@@ -74,8 +87,7 @@
 	<field name="slit_edges" type="NX_FLOAT" units="NX_ANGLE">
 		<doc>
 			Angle of each edge of every slit from the position of the
-			top-dead-center timestamp sensor, anticlockwise when facing
-			away from the source.
+			top-dead-center timestamp sensor.
 			The first edge must be the opening edge of a slit, thus the last edge
 			may have an angle greater than 360 degrees.
 		</doc>
@@ -93,8 +105,7 @@
 	<field name="beam_position" type="NX_FLOAT" units="NX_ANGLE">
 		<doc>
 			Angular separation of the center of the beam and the
-			top-dead-center timestamp sensor, anticlockwise when facing
-			away from the source.
+			top-dead-center timestamp sensor.
 		</doc>
 	</field>
 	<field name="radius" type="NX_FLOAT" units="NX_LENGTH">
@@ -140,9 +151,9 @@
             the source. The reference point in the x and y axis is the point on this surface which is the
             centre of the axle which the disk is spinning around. The reference plane is orthogonal to
             the z axis and its position is the reference point on that axis.
-                    
+
             Note: This reference point in almost all practical cases is not where the beam passes though.
-                    
+
             .. image:: disk_chopper/disk_chopper.png
                 :width: 40%
         </doc>