Force meter
A force meter is an instrument to measure the magnitude of a force. This is often just a spring contained within a cylinder that has a scale to mark the extension of the spring produced by the force. In the International System of Units, the unit of force is the newton (symbol N). A force meter that measures force in newtons may be referred to as a newtonmeter.
Bryan Kibble
In 1990, the Mark II watt balance was built, with a view to measuring the Planck constant accurately enough to redefine the S.I. unit of the kilogramme from fundamental constants. Such an instrument equalises one force with another, specifically the weight of a [one-kilogramme, typically] test mass and the force produced by an electric current in a moving coil in a magnetic field. The magnitude of the upward force on the coil is controlled by changes to the current. The power of the moving mass is equal to the product of the current and potential difference measured in the coil, hence the term 'watt' balance (as the S.I. unit of power is the watt (W)).