What Devise Used To Measure Mass?

A Forward mass detector (named for Robert L, Forward, scientist and Science Fiction author) is the most commonly used device for this purpose. It is also known as a rotating cruciform gravity gradiometer. The principle behind it is quite simple - getting the implementation right is tricky. Essentially, two beams are crossed over and connected with an axle through their crossing point. They are held at right angles to each other by springs. They have heavy masses at the ends of the beams, and the whole assembly spun around the common axle at high speed. The angle between the beams is measured continuously, and if it varies with a period half that of the rotation period, it means that the detector is experiencing a measurable gravitational field gradient.