The calibrations on a pressure gauge.
The fourth (yellow), is for touchscreen calibration.
The calibration of ammeters is best conducted by means of a series of standard low resistances and of a potentio meter.
These definitions provide a basis on which the calibration of amperemeters can be conducted.
This can be determined by a direct calibration, by inserting a known quantity of water at a known temperature and observing the contraction, or weighing the mercury drawn into the apparatus.
After this event the Calibration Curve.