diff --git a/script/keithley.py b/script/keithley.py
index 92c0b466..ec4484dd 100644
--- a/script/keithley.py
+++ b/script/keithley.py
@@ -1,4 +1,5 @@
 import ch.psi.pshell.epics as epics
+import math
 
 class Keithley(object):
     RANGE_STATES = ['AUTO', '20 mA', '2 mA', '200 uA', '20 uA', '2 uA', '200 nA', '20 nA', '2 nA', '200 pA', '20 pA']