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What is the protractor head used for?

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A blue protractor head being used to set the angle of the rule; combination square set, ruler, blade The protractor head can be used to determine specific angles, as, unlike a square head, the protractor is marked with the angles.
Four 180 degree angles; protractors 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.
A protractor head being used off the rule to measure the angle of a sloped surface; combination square set When taken off the rule, it can be used to measure the angle of a slanted edge.
A protractor head with a spirit level included; combination square set Spirit levels may also be found in protractor heads.