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.
Net force
A force is known as a bound vector—which means it has a direction and magnitude and a point of application. A convenient way to define a force is by a line segment from a point "A" to a point "B". If we denote the coordinates of these points as A=(A, A, A) and B=(B, B, B), then the force vector applied at "A" is given by
The length of the vector B-A defines the magnitude of F and is given by