How to measure diode voltage drop?

For VB series:

Turn the multimeter to the diode gear, the positive test pen is connected to the place where the circle is drawn, and the negative test lead isconnected to U, V, W in turn, and measure the voltage drop of the tube.(When measuring, the positive test pen needs to be pressed down hard to break the insulator to measure the value.)

For VM series:

Turn the multimeter to the diode gear, the positive test pen is connected to the place where the circle is drawn, and the negative test lead is connected to U, V, W in turn, and measure the voltage drop of the tube