Innova 3320 multimeter calibration
The other answer is right, adjust VR1 with a tiny screwdriver. Clockwise is lower voltage and counter is increase. Tested using DCV function. You should use a voltage reference module, but I just used the readings from 2 other meters that seemed accurate and adjusted it likewise. The other 2 meters have a thousandths place, this 3320 only has 2 digits. And we don't know what the other 2 VR2 and VR3 are.