The protractor head can be used to determine specific angles, as, unlike a square head, the protractor is marked with the angles.
Quite a few are marked up to 180 degrees and may be marked in both directions, allowing the user to determine the angle without having to work it out by hand (a process called “direct reading”). However, different manufacturers may have different designs.
When taken off the rule, it can be used to measure the angle of a slanted edge.
Spirit levels may also be found in protractor heads.
