Note: This tech tip is for the times when a calibration gets so far out of adjustment that you can’t get the calibration back in to proper range.
Turn the zero adjustment (center screw) clockwise, or counter clockwise, until it becomes hard to turn or starts to bind. Once it starts to bind stop turning. Then turn adjustment screw (9) complete turns in the opposite direction.
Turn the span adjustment (outer ring) in the necessary direction so that (2) threads are showing as the photo indicates.
The above procedures will set the zero and span adjustments to the middle of their respective adjustment ranges and should be a good point to start calibration.