Imran,
Immediately upon power up my display shows "U 2.1" for about 2 seconds. Then it will display either inches or mm. If I want to change the units, I have to power off and then hold the reset button while powering back on. Sometimes the calibration is lost and sometimes it is not, however it feels like most of the time the calibration is lost when powering back up.
Investigating the reset button is a good idea, as that's how it would change between units, perhaps something is happening there? Though once the AD741 is powered on the units aren't changed or reset.
-Ameer
