diff --git a/site_ansto/instrument/hipd/config/hmm/hmm_configuration.tcl b/site_ansto/instrument/hipd/config/hmm/hmm_configuration.tcl
index 67f42792..a19468a8 100644
--- a/site_ansto/instrument/hipd/config/hmm/hmm_configuration.tcl
+++ b/site_ansto/instrument/hipd/config/hmm/hmm_configuration.tcl
@@ -121,7 +121,9 @@ proc ::histogram_memory::isc_initialize {} {
 
     detector_active_height_mm  203.2
     detector_active_height_mm lock
-    detector_active_width_mm 1524
+#   detector_active_width_mm 1524
+#   Adjusted to give 121 degrees
+    detector_active_width_mm 1537.426
     detector_active_width_mm lock
     detector_radius_mm 728.0
     detector_radius_mm lock