Question

The vernier scale in which 10 divisions of the vernier scale is equal to 9 divisions of the main scale is called ____

• A. Retrograde vernier
• B. Direct vernier
• C. Extended vernier
• D. Double vernier

Answer 1

The correct option is B Direct vernier

• The direct vernier has divisions that are slightly shorter than those of the main scale. Thus, n division on the vernier scale is equal in length to (n - 1) division on the main scale.

• $nV=(n-1)S$

Note:

Retrograde vernier: In retrograde vernier, divisions are slightly longer than those of the main scale. So n divisions of the vernier scale are equal to (n +1) divisions on the main scale


$nV=(n+1)S$

Where n = Number of divisions on the vernier

V = Value of the smallest division on the vernier

S = Value of the smallest division on the main scale

• Extended vernier: Divisions on the main scale may vary and it would then be difficult, if the vernier were of normal length, to judge the exact graduation where coincidence occurs. In this case, an extended vernier may be used here (2n -1) divisions on the main scale are equal to n divisions on the vernier so that,

$nV=(2n-1)S$

$V=\frac{2n-1}{n}S=(2-\frac{1}{n})S=\frac{S}{n}$

The difference between two main scale-spaces and one vernier space = 2S-V

• Double vernier: In measuring angles (vertical or horizontal), vernier may be moved in either direction on fixed main scale. For such measurement double vernier are used in which graduations are in both directions.