diff --git a/PythonServer/pos-python-server.py b/PythonServer/pos-python-server.py
index fdd0ed66dd5e28ded8f597cd3033e84cfb1c65c6..85a34975029d57d082b8913eec7c86ee0b027ca9 100755
--- a/PythonServer/pos-python-server.py
+++ b/PythonServer/pos-python-server.py
@@ -374,7 +374,10 @@ class epicsQuery(Thread):
 
                     if pv=='LEBT-010:PBI-Dpl-001:FIT1-Y_RBV':
                         y_data=list(instruments[pv].value)
-                        x_data=list(linspace(instruments['LEBT-010:PBI-Dpl-001:SPECT-MinWavelength'].value, instruments['LEBT-010:PBI-Dpl-001:SPECT-MaxWavelength'].value,  len(y_data)))
+                        pixel2lambda=(instruments['LEBT-010:PBI-Dpl-001:SPECT-MaxWavelength'].value-instruments['LEBT-010:PBI-Dpl-001:SPECT-MinWavelength'].value)/1024
+                        start_wave = instruments['LEBT-010:PBI-Dpl-001:SPECT-MinWavelength'].value + instruments['LEBT-010:PBI-Dpl-001:ROI1-MinX'].value*pixel2lambda
+                        end_wave = instruments['LEBT-010:PBI-Dpl-001:SPECT-MinWavelength'].value + (instruments['LEBT-010:PBI-Dpl-001:ROI1-MinX'].value+instruments['LEBT-010:PBI-Dpl-001:ROI1-SizeX'].value)*pixel2lambda
+                        x_data=list(linspace(start_wave, end_wave,  len(y_data)))
                         instruments_return_dict[pv]['value']=list(zip(x_data,y_data))
                         continue