diff --git a/site_ansto/instrument/config/hmm/hmm_configuration_common_1.tcl b/site_ansto/instrument/config/hmm/hmm_configuration_common_1.tcl
index cbe97274..24d0b707 100644
--- a/site_ansto/instrument/config/hmm/hmm_configuration_common_1.tcl
+++ b/site_ansto/instrument/config/hmm/hmm_configuration_common_1.tcl
@@ -390,7 +390,7 @@ namespace eval histogram_memory {
     if [ catch {
       set det_height_mm [SplitReply [detector_active_height_mm]]
       set max_chan [OAT_TABLE Y -getdata MAX_CHAN]
-      set scale_factor [expr {$det_height_mm / $max_chan}]
+      set scale_factor [expr {1.0 * $det_height_mm / $max_chan}]
       set offset 0.0
       ::histogram_memory::calc_axis "y_pixel_offset" $scale_factor $offset [OAT_TABLE Y -getdata BOUNDARIES]
       if {$args == "-get_data_ref"} {
@@ -426,7 +426,7 @@ namespace eval histogram_memory {
     if [ catch {
       set det_width_mm [SplitReply [detector_active_width_mm]]
       set max_chan [OAT_TABLE X -getdata MAX_CHAN]
-      set scale_factor [expr {$det_width_mm / $max_chan}]
+      set scale_factor [expr {1.0 * $det_width_mm / $max_chan}]
       set offset 0.0
       ::histogram_memory::calc_axis "x_pixel_offset" $scale_factor $offset [OAT_TABLE X -getdata BOUNDARIES]
       if {$args == "-get_data_ref"} {