Sine Bar & Gauge Blocks

A sine bar turns an angle into a height you can build from gauge blocks: sin θ = H / L. Simple trig, universally used in inspection, and very easy to get backwards — the height goes under one roll, and the length is the roll centre distance, not the bar.

Sine bars lose accuracy above about 45° because the sine curve flattens — a small height error becomes a large angle error. Use an angle block or a sine plate beyond that. Keep stacks short; every wrung joint adds error.