ABSTRACT
The angle is the ratio of circumference to the radius of the circle. Each degree is divided into 60 min of an arc and each minute is divided into 60 s of an arc. Therefore, angle measurement is linked to the length and hence is traceable to the standard meter through various kinds of techniques and instrumentation. Angle gauges with different tolerances are used to transfer secondary length standards to the laboratories and industry. The angle of the prism is measured by comparing it with an angle standard. Both are placed side by side and both reflect the beam from the autocollimator. Shift between the two cross-wire images will give the difference in angles. Angle encoders are available that could be used for angle measurement with proper instrumentation. The angle of a wedge plate can be determined by two ways using either a Fizeau interferometer or a Twyman–Green interferometer.
