analog multimeter cal

[Kyoungmin Kim]

hi, guys!
I have a another question about analog multimeter.
In according to TO 33K1-4-141-1, they said "Mechanically zero TI meter pointer when required"
I want to know when is when....
When I calibrated AN/PSM-37, I changed function like a DC or AC the zero has moved....
When it changed, do I have to readjust the zero?

[ck454ss]

"When Required" is when it isnt reading zero. 

Yes if your zero shifts its needs to be readjusted but you also need to make sure thats "Normal".  Usually your mechanical zero shouldnt drift when swithcing functions.

[measure]

In my experience, unless otherwise stated in the manufacturer's documentation. analog meters are intended to be zeroed with the power off and after any remaining residuals have dissipated. When powered up and operating, a change in 'zero' reading when changing function is not uncommon, particularly when switching to AC, due to floor noise in the RMS converter (assuming RMS detection). Readjusting the zero at this point is much more likely to cause the reading to be less accurate instead of more, the latter generally being the desired goal.