Figure 1: Vernier scale.
Figure 2: Vernier Bevel Protractor.
Vernier Bevel Protractor is an instrument used to measure angles to an accuracy of 5 minutes (5’) or 1/12 of one degree. The vernier principle is applied in angular measurements. The vernier protractor includes number of attachments, that make it possible for wide range of measurements.
The main scale is graduated in degrees. On some instruments, this scale is on the body of the instrument itself while on other instruments, the graduations are on the rotating turret. The vernier scale has 24 divisions. 12 divisions are on each side of the zero index line. The 24 vernier scale divisions are numbered from 60 to 0 and 0 to 60, as shown in figure (1). Each vernier graduation represents 5’.
In angular measurements. it is important to read vernier scale reading. When the angle is an exact degree. the index line on the vernier scale. coincides with graduation on the main scale. However, if the angle is more than an exact number of degrees. the fractional value (in 5’ increments) is read on the vernier scale.