A sine gauge, also known as a sine ruler, is a gauge that uses sine to measure angles and taper angles. It mainly consists of a steel rectangular prism and two steel cylinders of the same diameter fixed at its two ends. The distance L between the axis lines of two cylinders is generally 100 millimeters or 200 millimeters. The picture shows the use of a sine gauge to measure a cone gauge. In a right angled triangle, sinα＝H/L， In the formula, H is the size of the measuring block group, calculated based on the nominal angle of the measured angle. The error of the measured angle can be calculated based on the difference between the readings of the micrometer at both ends. Sine gauges are generally used to measure angles less than 45 °, and their accuracy can reach 3 "to 5" when measuring angles less than 30 °.