velocity mode of precision laser called an interferometer shown here in green is used to measure the position and velocity of the coil. the aim is to measure the voltage that is created in the process. then we need gravitational acceleration small g. 9.81 meters per 2nd per 2nd if you know all these things very precisely you can calculate the numerical value for h. the math isn't complicated in reverse if you know the value of h. the planck constant you can specify a kilogram. the planck scales from germany will work in exactly the same way they're basically a water bottle and on the left is the laser interferometer on the right is the balance based on the principle of electromagnetic force compensation but it's