How to Use a Square Head Protractor

A square head protractor most commonly refers to a specific type of measuring device employed by a draftsman or architect to measure an existing angle on paper. It is a handy tool for transferring or reading angles on blueprints, mechanical drawings or building plans. The flat, adjustable tool can also be used in the field to record numerical values for an existing angle. In certain situations (obtuse angles) it can be used like a bevel gauge.

Square head protractor
Pencil
Blueprints or building plans

Instructions

- 1
  Loosen the adjusting nut that holds the swing arm tight to the plate. The long arm should now slide back and forth.
- 2
  Pull out a blueprint, mechanical drawing or building plan and locate any angle. To get an accurate value for the angle, place the bottom edge of the rectangular plate on one side of the angle and the long swing arm on the opposite side. Make sure both edges of the protractor line up precisely with each line. Then, make the numerical reading. It will be between 0 and 180 degrees.
- 3
  Tighten the nut where the long arm joins the rectangular plate.
- 4
  Remove the square from the spot on the drawing and transfer the angle to a board, piece of metal or another part of the drawing.

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