The maximum demand ammeters indicate the thermal/time characteristics of the load, The high torque of the thermal movement drive a red slave pointer linked to the instruments is pointer. The slave pointer will remain at the maximum value reached for a subsequent reading until being manually reset by knob to the position of the instrument pointer.
The moving coil PF meter used to monitor changing power factor condition on balanced load & unbalance system. The power factor is indirectly by measuring the phase angle Ø between current & voltage . However the indicators are calibrated in values of cos of the angle Ø.