After the change in the design of the ammeter, the price of the pressure of the device changed

After the change in the design of the ammeter, the price of the pressure of the device changed, so a new scale must be applied to it. How to do this using a different ammeter?

To change the design of the ammeter, a resistance shunt is used. To calibrate the ammeter scale in practice, use a second working ammeter. The ammeters are connected in series with each other, because the internal resistance of the frames is very small and the measurement error will also be small. With a rheostat, the current in the measured circuit is changed several times and marks are made on a new scale of the ammeter under test. It is necessary to measure the maximum deviation of the ammeter arrows.