Question

reflector combined with autocollimator can measure

Answer 1

Reflectors and Auto-collimators are Optical Instruments that are used for Angular Measurement in Metrology.

The autocollimator helps in measuring the deviation in between the emitted beam and the reflected beam. There are 2 images that are produced in the auto-collimator and their separation is used for directly reading the angular error. When there is a reflector, a small of light gets reflected which also helps in detecting the angular measurements.