The head of the multimeter is a sensitive galvanometer. The dial on the head is printed with various symbols, scale marks and values. The symbol A-V-Ω indicates that the ammeter is a multimeter that can measure current, voltage and resistance. There are multiple scale lines printed on the dial, among which the one marked with "Ω" on the right is the resistance scale line, the right end is zero, the left end is ∞, and the scale value distribution is uneven. The symbol "-" or "DC" means direct current, "~" or "AC" means alternating current, and "~" means the scale line shared by AC and DC. Several rows of numbers under the scale line are the scale values corresponding to the different positions of the selector switch.

Inside the multimeter, some non-pure resistance components are involved in the measurement of AC, such as the pointer coil of the pointer meter, the DC isolation capacitor of the digital meter, etc., and its impedance is related to the frequency and waveform of the AC. Therefore, the calibration of the multimeter is calibrated with a certain frequency and waveform of alternating current as the standard. If you use it to measure alternating currents of other frequencies and waveforms, the readings will be inaccurate.