a handful of these scales worldwide this one is in the united states at the national institute of standards and technology. the high precision scale is based on the principle of electromagnetic force compensation this is how it works the gravitational force of a test mass is balanced with an electromagnetic force the magnetic field is provided by a permanent magnet a coil of wire is immersed in that field. it's like a coil in a loudspeaker and the coil is in a permanent magnetic field an electrical current is run through it to generate a force that force is used to balance the downward force of the weight it's a way to measure weight using an electrical current of. a mission in other words the electrical current is adjusted until the upward force on the coil perfectly balances the downward force of the weight the 2nd step is called the