How to use a multimeter to measure the quality of a half-section unidirectional thyristor

See the figure for the method. Use the R×10 position of the multimeter, connect the black test lead to the anode of the unidirectional thyristor, and the red test lead to the cathode. At this time, the unidirectional thyristor is cut off, and the multimeter pointer should be close to "∞"; when the switch S is closed, the needle should indicate a very small resistance value between 60 and 200Ω. This indicates that the unidirectional thyristor is triggered and turned on. When S is turned off, the multimeter needle does not return to zero (still on a number between 60 and 200Ω), indicating that the unidirectional thyristor being tested is normal. Some unidirectional thyristors have a large holding current, and the current of the multimeter is not enough to maintain its conduction. When the S tube is turned on, the multimeter pointer returns to "∞", which is also normal. If the resistance indicated by the multimeter is very small when S is not closed, or the needle does not move when S is closed (still pointing to ∞), it indicates that the quality of this unidirectional thyristor is too poor or it has been broken down, the pole is broken, and it cannot be used.