An apparatus used to measure the physical quantity is called the measuring apparatus. In physical sciences, engineering and quality assurance, measurement is obtaining and comparing the physical quantities of real-world objects.
In our everyday life, length is measured using a metre scale. Metre scales are calibrated in mm and cm. The least length measured by a metre scale is called the least count. The metre scale has the least count of 1 mm. This scale cannot be used to measure the size of smaller spherical objects more accurately. So, instruments like screw gauge and vernier caliper are used. The least count of vernier caliper and screw gauge is lesser than a metre scale.
The measurement of dimensions of a hollow object or a spherical object can be done using a vernier caliper. Vernier calipers can measure both the inner diameter and outer diameter of the objects.Vernier caliper has a main scale and a vernier scale. The main scale of the vernier caliper looks similar to the metre scale, it is calibrated in mm and cm. The left end of the main scale has an upper jaw and a lower jaw. These are called the fixed jaws. To the right side of the fixed jaws, the moveable upper jaw and lower jaws are fixed to the slider. The upper jaws are used in the measurement of the internal dimensions and the lower jaws measure the external dimensions. The depth of the object is measured using the thin bar on the right side of the main scale.
Least Count of Vernier Caliper
The least count of the vernier caliper can be easily calculated by finding the value of the smallest division on the vernier scale and the total number of divisions on the vernier scale. The vernier scale has a total of 10 divisions. The formula for least count of vernier caliper is given below
Least Count = Value of one smallest division on the main scale/Total number of vernier scale division
L.C = 1mm/ 10 = 0.1 mm = 0.01 cm
Both the jaws are made to touch by unscrewing the slider and then moving it to the left. If the zero marking of the main scale and the vernier scale coincides then the vernier caliper does not have any error. If the zeroes do not coincide then the vernier caliper possesses zero error. The zero error can be positive or negative.
If the zero of the vernier scale lies on the right side of the zero on the main scale then the error is positive. On the other hand, if the zero of the vernier scale lies on the left side of the zero of the main scale then the error is negative.
If the vernier caliper has a positive zero error, the reading will be more than the actual reading. Therefore the positive zero error should be subtracted to get the correct reading. In case of a negative error, the error value must be added to find the correct reading.