Gradutions on vernier bevel protractor
. main scale graduations on the disc
.the vernier scale graduations on the dial
. determine the least count of the vernier bevel protractor
The main scale graduations
For purpose of taking angular measurement, the full circumference of the disc is graduated in degrees.The 360degree are equal divided and marked in four quardrants, from 0 degree to 90 degree, 90 degrees to 0 degrees, 0 to 90 degrees and 90 degrees to 0 degrees. Every tenth division is marked longer and numbered. Each division represents 1 degree. The graduations on the disc are known as the main scale divisions. On the dial, 23division spacing of the main scale is equally divided into 12 equal parts on the vernier. Each 3rd line is marked longer and numbered as 0,15,30,45,60. This constitutes the vernier scale. Similar graduation are marked to the left of 0 also.
One vernier scale division (MSD)The least count of the vernier bevel protractor
When the zero of the vernier scale coincides with the zero of the main scale, the first division of the vernier scale will be very close to the 2nd main scale division
Hence, the least count is
2 MSD- 1 VSD
i. e the least count=2°-23°/12
=1°/12=5°
For any setting of the blade and stock, the reading of the acute angle and the supplementary obtuse angle is possible, and the two sets of the vernier scale graduations on the dial assist to achieve this.
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