Unit of electric current: ampere (A)
 The ampere, symbol A, is the SI unit of electric current. It is defined by taking the fixed numerical value of the elementary charge
e to be 1.602 176 634 ×10^{−19} when expressed in the unit C, which is equal to A s, where the second is defined in terms of ∆ν_{Cs}.

Unit of electric potential: volt (V)
 The volt is the potential difference between two points of a conducting wire carrying a constant current of 1 ampere, when the power dissipated between these points is equal to 1 watt.

Unit of electric resistance: ohm (Ω)
 The ohm is the electric resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere, the conductor not being the seat of any electromotive force.

Practical realization of the ampere, volt and ohm
In practice, the ampere A can be realised:
 by using Ohm’s law, the unit relation A = V/Ω, and using practical realizations of the SI derived units the volt V and the ohm Ω, based on the Josephson and quantum Hall effects, respectively
 by using a single electron transport (SET) or similar device, the unit relation A = C/s, the value of
e given in the definition of the ampere and a practical realization of the SI base unit the second s;
 by using the relation
I =
C·dU/dt, the unit relation A = F·V/s, and practical realizations of the SI derived units the volt V and the farad F and of the SI base unit second s.
In practice, the volt can be realised:
 using the Josephson effect and the following value of the Josephson constant:
K_{J} = 483 597.848 416 984 GHz V^{–1}. This value has been calculated to 15 significant digits.
In practice, the ohm can be realised:
 by using the quantum Hall effect in a manner consistent with the CCEM Guidelines and the following value of the von Klitzing constant
R_{K} = 25 812.807 459 3045 Ω. This value has been calculated to 15 significant digits.
 by comparing an unknown resistance to the impedance of a known capacitance using.
Unit of capacitance: farad (F)
 The farad is the capacitance of a capacitor between the plates of which there appears a potential difference of 1 volt when it is charged by a quantity of electricity of 1 coulomb.

Unit of electric inductance: henry (H)
 The henry is the inductance of a closed circuit in which an electromotive force of 1 volt is produced when the electric current in the circuit varies uniformly at the rate of 1 ampere per second.

Electrical metrology calibration services