The resistance of a conductor is usually represented by the letter R. The unit of resistance is ohm, abbreviated as ohm, and the symbol is Ω (Greek letter, transliterated into pinyin as ōu mī ga), 1Ω=1V/A. Larger units include kiloohms (kΩ) and megaohms (MΩ) (M=million, i.e. 1 million).

The basic unit of electric current is ampere. 1 ampere is defined as: two infinitely long parallel straight wires 1 meter apart in a vacuum are passed with equal constant current. When the force acting on each meter of the wire is 2×10^-7N, the current in each wire is 1 ampere.

The main unit of voltage in the International System of Units is the volt (V), abbreviated as V, represented by the symbol V. [1] 1 volt is equal to 1 joule of work done on every 1 coulomb of charge in the voltmeter, that is, 1 V = 1 J/C. Strong voltage is usually measured in kilovolts (KV), while weak voltage can be measured in millivolts (mV) or microvolts (μV).