Vernier scales
Vernier Scale: These scales, like diagonal scales, are used to read to a very small unit with great accuracy. It consists of two parts - a primary scale and a vernier. The primary scale is a plain scale fully divided into minor divisions. As it would be difficult to sub-divide the minor division in an ordinary way, it is done with the help of the vernier. The graduations on vernier are derived from those on the primary scale. The figure shows a part of a plain scale in which length A-O represents 10 cm. if we divide A-O into ten equal parts, each will be of 1 cm. now it would not be easy to divide each of these parts into ten equal divisions to get measurements in millimeter. Now if we teak a length BO equal to 10 + 1 = 11 such equal parts, thus representing 11 cm, and divide it into ten equal divisions, each of these divisions will represent 11 / 10 -1.1 cm. The difference between one part of AO and One division of BO will be equal 1.1-1.0=0.1 cm or mm. This difference is calle...