Hi,
With ET44/4510 it is as follows:
If you want to do a short calibration, short-circuit the test lead and press the CAL button - and hold it down until the short cal message appears.
A timer then runs backwards from 20 to zero.
-If you want to do an Open Calibration, leave the test leads open and press the CAL button - and hold it down until the Open Cal message appears.