I could not find anything looks like something for calibration in the
voltmeter. Thanks for the tip though.

Jay Chan

Jay,
I do not know about the meter you have. But most analog meters
including analog multimeters have a screw at the pivot point of the
needle.

Look at the enlarged picture of the meter.

http://www.go2marine.com/g2m/action/...1&WT.mc_id=fr1

Paul