(Gauge Calibration)
It depends on the year, make, model. Some gauge needles can be removed, re-installed and calibrated with the cluster powered off.
Other cluster clusters require the ignition to be on to re-install the gauge needles. Then there are certain clusters that we highly advise against removing the needles to prevent further damage.
On clusters that don't need any ignition power to calibrate, see where the needles naturally stop. Be careful not to force the needles otherwise, they can de-calibrate. then use removable tape and a sharpie to indicate where they stop. When you re-install the needles you can re-calibrate the gauge needles to the stopping point indicated.
For the clusters that need ignition to re-calibrate, the large gauges are straightforward since they will simply need to be re-installed right on the stoppers. Be careful because those easily break. You can use a plastic trim remover or fork to remove the needles.
As for the smaller gauges, those are a little more tricky since they can be going to various places. The easiest way to do it is by hooking up a scan tool and reading the values of those gauges. Then you can install them according to what the sensor readout on the the OBDII scan tool displays.