The Vernier Caliper consists of a thin long steel scale graduated in cm and mm called main scale. To the left end of the main scale an upper and a lower jaw are fixed perpendicular to the bar. These are named as fixed jaws. To the right fixed jaws, a slider with an upper and a lower moveable jaw is fixed. The slider can be moved or fixed to any position using a screw.

The vernier scale is marked on the slider and it moves along with the moveable jaws and the slider. The lower jaws are used to measure the external dimensions and the upper jaws are used to measure the internal dimensions of the objects. The thin bar attached to the right side of the vernier scale is used to measure the depth of hollow objects.

USAGE OF VERNIER CALLIPER

The first step in using vernier calliper is to find out its least count, range and zero error.

LEAST COUNT

Least count of the instrument (L.C) is equal to the value of one main scale division divided by Total number of vernier scale division.
The main scale division will be in centimetre, further divided into millimetre. The value of the smallest main scale division is 1mm. In the vernier scale there will be 10 divisions.
Therefore L.C is equal to 0.01cm.

ZERO ERROR

Unscrew the slider and move it to the left, such that both the jaws touch each other. Check the zero marking of the main scale coincides with that of the zero of the vernier scale. If they coincide then there is no error. If they do not coincide with each other, the instrument is said to possess zero error. Zero error may be positive or negative. If the zero of a vernier is shifted to the right of main scale, it is called positive error. On the other hand, if the zero of the vernier is shifted to the left of the zero of main scale, then the error is negative

POSITIVE ZERO ERROR

That the zero of the vernier scale is shifted to the right of the zero of the main scale. In this case the reading will be more than the actual reading. Hence, this error should be corrected. In order to correct this error, find out which vernier division is coinciding with any of the main scale divisions. Here, fifth vernier division is coinciding with a main scale division. So, positive zero error = +5LC = +50.01 = 0.05cm and the zero correction is negative. Hence, zero correction is -0.05cm.

NEGATIVE ZERO ERROR

That the zero vernier scale shifted to the left of the zero of the main scale. So, the obtained reading will be less than the actual reading. To correct this error we should first find which vernier division is coinciding with any of the main scale divisions, as we found in the previous case. In this case, the sixth line coinciding. To find negative error, we can count backward (from 10). Here, the fourth line is coinciding. Therefore, negative zero error= -4 × LC = -4×0.01 = -0.04cm. Then zero correction is positive. Hence, zero correction is +0.04cm.

DIGITAL VERNIER CALIPERS

In this digital world, the digital version of vernier caliper are available. Digital vernier caliper has a digital display on the slider, which calculates and displays the measured value. The user need not manually calculate the least count, zero error etc.,