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Construction of Vernier Calliper

Vernier caliper is a measuring device used to measure precise increments between two points.

• Main Scale; Main scale is graduated in cm and mm.

• Vernier Scale; It slides on the main scale. On Vernier scale 0.9cm is divided into 10 equal parts.

• Jaws; Two inside jaws (Upper) Two outside jaws (Lower)

• Least Count: Least count (L.C) is the smallest reading we can measure with the instrument. L.C = one main scale division – one vernier scale division L.C = 1mm – 0.09mm = 0.1 mm = 0.01 cm

Zero Error in Vernier Calliper

When the jaws are closed, the vernier zero mark coincides with the zero mark on its fixed main scale. Before taking any reading it is good practice to close the jaws or faces of the instrument to make sure it is reading zero. If not then note the reading. This reading is called “zero error”. The zero error is of two types (i) positive zero error and (ii) negative zero error. Positive Zero Error If the zero on the vernier scale is to the right of the main scale, then the error is said to be positive zero error and so the zero correction should be subtracted from the reading which is measured. Negative Zero Error If the zero on the vernier scale is to the left of the main scale, then the error is said to be negative zero error and so the zero correction should be added from the reading which is measured.

ReadingVernier Calliper The Vernier calliper consists of a main scale fitted with a jaw at one end. Another jaw, containing the vernier scale, moves over the main scale. When the two jaws are in contact, the zero of the main scale and the zero of the vernier scale should coincide. If both the zeros do not coincide, there will be a positive or negative zero error.

After calculating the least count place the object between

the two jaws.

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Record the position of zero of the vernier scale on the main scale (3.2 cm in figure below).

You will notice that one of the vernier scale divisions coincides with one of the main scale divisions. (In the illustration, 3rd division on the vernier coincides with a MS division).

Reading of the instrument = MS div + (coinciding VS div x L.C.)

= 3.2 + (3 x 0.01)

= 3.2 + 0.03

= 3.23 cm

To measure the inner and outer diameter of a hollow cylinder or ring, inner and oute r callipers are used. Take measurements by the two methods as shown in figure below.