Rulers were used for straight lines, compasses for circles, and protractors for angles. Rulers, protractors and compasses can be taken into the examination. They are often purchased in packs with protractors and compasses. Radian-scale protractors measure angles in radians. This company was established in the 1890s and made rulers, blackboard triangles, protractors, etc. Drafting machines use pre-calibrated scales and built in protractors to allow accurate drawing measurement. Some precision protractors further divide degrees into arcminutes. If fitted with protractors, it could be used to measure angles. Subtracting the detractors from the protractors gives the calculation of advocacy. Some protractors are simple half-discs. Most protractors are divided into 180 equal parts.