How a digital multimeter measures current
1. Disconnect the circuit;
2. The black test lead is inserted into the com port, and the red test lead is inserted into the mA or 20A port;
3. Turn the function rotary switch to A~ (AC), A- (DC), and select the appropriate range;
4. Disconnect the line under test, connect the digital multimeter in series with the line under test, the current in the line under test flows from one end into the red test lead, flows out through the black test lead of the multimeter, and then flows into the line under test;
5. Turn on the circuit;
6. Read the display number.
