The kilogram is the last SI base unit defined in terms of artificial prototype, by which we can not verify the universality of definition.Therefore, there are studies to improve absolute determination concerning electrical quantity aiming a new definition of kilogram in terms of the fundamental constants.

Figure 1: Schematics of the superconducting magnetic levitation system.

The method using superconducting magnetic levitation in NRLM is based on the concept of quasi-static energy injection process, where the energy injected from external source is equal to the sum of increase of magnetic energy and increase of gravitational.The absolute value of magnetic flux quantum is calculated from the energy equation by measuring the flux linking to coil and coil current in the unit of . In actual, quasi-static process is not necessary since above calculation can be performed on the data in equilibrium of the system. Then, actual process consists of two repetitive parts: (1) to increase the flux linking to coil by a certain amount in terms of Josephson voltage, (2) to measure the coil current and the vertical displacement of the center of gravity of floating body in equilibrium. Further details of method has been described elsewhere.