Is there a theoretical basis for carpenters to check whether the adjacent sides of the door frame are vertical with crutches?

The door frame is quadrangular, with long sides, etc., which ignores the technical errors of craftsmen when making door frames. If the corner of the door frame can match the crutch, it can be concluded that the two adjacent edges of the door frame are perpendicular to each other. The theoretical basis is that crutches are right-angled, that is, angles are right-angled, while quadrilaterals are equal in opposite sides, one angle is right-angled, and the other three angles are right-angled.