Why does the multimeter display close to 0 when the test leads are not inserted, and more than 100 mV when the test leads are inserted?
This is because when the multimeter is plugged into the test lead but not connected to the signal under test, the test lead is similar to an antenna at this time, and the noise of the environment will be tested.
By inserting the test leads, it is equivalent to inserting the antenna on the front panel of the multimeter, which will detect the received noise. With the test leads shorted together, the multimeter should read very close to 0.
