This document discusses four types of scales used for measurement: plain scales, diagonal scales, chord scales, and vernier scales. Plain scales represent units and tenths or meters and decimeters. Diagonal scales allow measurement of units, tenths, and hundredths using similar triangles. Chord scales are used to measure or set off angles and are marked on protractors or wooden scales. Vernier scales have two approximating scales, a fixed primary scale and a movable vernier scale, where the least count is determined by the number of divisions on each scale.