$$P - 4,\,\,Q - 3,\,\,R - 1,\,\,S - 2$$

$$P - 1,\,\,Q - 2,\,\,R - 3,\,\,S - 4$$

$$P - 1,\,\,Q - 4,\,\,R - 3,\,\,S - 2$$

$$P - 4,\,\,Q - 3,\,\,R - 2,\,\,S - 1$$

Measure small angular displacements on flat surfaces

Compare known and unknown dimensions

Measure the flatness error

Measure roundness error between centers