Digital three phase voltmeters are designed to monitor AC voltage value continuously.When the device is energized, it shows the value of the phase-neutral or phase AC voltage coming to Vinputs constantly on the display.When there is voltage values belonging to phases L1,L2 and L3 on the screen, when the SELECT button is pressed, the device displays the L12,L23,L31 phase-to phase voltage values on the screen.When SELECT button is pressed again.The device will show the phase sequence.