Fixed timestep calculation error for PicoSpope 4444

Author: csi-bbio

picoscope/ps4000a.py

@@ -457,7 +457,7 @@ def getTimestepFromTimebase(self, timebase):
             dt = (timebase + 1) / 8.0E7
         elif self.model == '4444':
             if timebase < 3:
-                dt = 2.5 ** timebase / 4.0E8
+                dt = 2 ** timebase / 4.0E8
             else:
                 dt = (timebase - 2) / 5.0E7