Sine Bar
A sine bar is a precision measurement tool built of finely ground or lapped steel, used to measure angles for parts or for measuring angled parts. Typically, a sine bar is no wider than 1 inch and is designed with a precision cylinder located at each end resting against stops that are machined into the bottom surface of the tool. A sine bar is used with gauge blocks to hold the tool at an angle that forms an ABC right triangle. The formed triangle is then used to calculate the angle measurement using trigonometry and the formula ϴ = asin(BC/AB), hence their name.