diff --git a/hp4155/ADU for double gate devices/lib/measurements.py b/hp4155/ADU for double gate devices/lib/measurements.py
index a0c9f9e7d6574c05c647780a00dbf0b0669088c4..5095055ea67bfd47bf4c4324fd9c7d361bfa3204 100644
--- a/hp4155/ADU for double gate devices/lib/measurements.py	
+++ b/hp4155/ADU for double gate devices/lib/measurements.py	
@@ -334,7 +334,7 @@ def Transfer_BOTH(VTG,VBG,VDS,integration,sample,device):
     ratio,offset = calculate_line(VTG,VBG)
 
     # update VBG step
-    VBG["step"].value = Decimal(str(ratio)) * Decimal(str(VBG["step"].value))
+    VBG["step"].value = Decimal(str(ratio)) * Decimal(str(VTG["step"].value))
 
     vard = device.vard_dict()
     vard.update(