Set square
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A set square or triangle is an object used in engineering and technical drawing, with the aim of providing a straightedge at a right angle or other particular planar angle to a baseline.
Variant of larger TZ-Dreieck with extra markings
Navigational Cras protractor (foreground)
T-square
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A T-square is a technical drawing instrument used by draftsmen primarily as a guide for drawing horizontal lines on a drafting table. The instrument is named after its resemblance to the letter T, wit
Drafting board with a T-square and set square