Least Count

In the science of measurement, the smallest and most precise value in a measured quantity that can be resolved on the instrument’s scale is referred to as the least count of the instrument.

The accuracy of an instrument is connected to its least count value; an instrument that can measure smaller changes in a value relative to another instrument has a smaller “least count” value and is therefore more exact than the other instrument. Putting it simply, we may define the least count of an instrument as the smallest number that can be obtained from it using the least amount of data. Consider that the smallest distance that can be measured from a metre scale is 1 mm, and that thus the least count that can be measured from the scale is 1 mm.

Least Count in equipment’s

Only scale markings reflecting the hours of daylight are available on a sundial; a count of one hour would be the least count of the sundial. A stopwatch used to time a race might be accurate to a tenth of a second, which is the least count of that particular stopwatch.  Because it has more intervals in each hour of elapsed time than the sundial, the stopwatch is more precise or we can say that a stopwatch is a  better tool for measuring time intervals. In order to obtain precise readings from instruments such as vernier callipers and screw gauges, which are utilised in many experiments, the least count of an instrument is one of the most critical tools to have.

Least Count Vs Accuracy

The instrument’s accuracy and precision are measured by the least count. The accuracy of an instrument will increase in direct proportion to the lowest count. The terms “least count” and “accuracy” should not be confused; they refer to two very separate concepts. When it comes to measuring accuracy, it refers to how near an instrument may come to a specific value.

Vernier Calliper

A Vernier Calliper is a device that is used to take a linear measurement with extremely high accuracy. Because of their excellent accuracy, Vernier Callipers are very commonly employed in scientific laboratories.

A Vernier Calliper is made up of two scales that measure distance.

Main scale of the Vernier calliper is similar to that of a ruler; on one side, it has graduations in mm and centimetres (cm), and on the other side, it has graduations in inches (inches).

It is the Vernier scale that is to be measured in comparison to the Main scale of the Vernier Calliper. The main scale reading is taken as the first reading on the main scale that is to the left of the zero of the Vernier scale, which is the first reading on the main scale. The vernier scale is a movable scale that is used in precision work. In addition to moving parallel to the main scale, it allows readings to be taken on the main scale of the vernier calliper that are fractions of a division. The mark made on the Vernier scale that exactly corresponds to a mark made on the main scale is referred to as the vernier scale reading.

The linear measurement is aided by the use of both the main scale and the vernier scale.

The jaws of a Vernier calliper are also an important component. A vernier calliper is a calliper with two jaws. In this case, the lower jaws are referred to as the outside jaws, and they are used to measure the length of a rod, the diameter of a sphere, and the exterior diameter of a cylinder, among other things. The higher jaws of the calliper are referred to as the inside jaws, and they are used to measure the internal diameter of a hollow tube or cylinder. The thin strip in a Vernier calliper is used to measure the depth of objects such as beakers, which is a precise measurement. The calliper can be fixed at any location on the main scale with the use of screws on the vernier scale.

Zero Error

As soon as the two jaws are closed, check to see that the zero marks on the main scale and the zero marks on the vernier scale are the same. If they are not, then there is no zero error; otherwise, it is taken into consideration when performing linear measurements on the main scale.

The term “zero error” refers to the situation in which a measuring instrument takes a reading when no reading is expected. When a zero on the main scale does not correspond with a zero on the Vernier scale, this is referred to as Vernier Calliper zero error.

Least count of Vernier Calliper

The lowest division on the main scale divided by the least number of divisions on the Vernier scale is the least count of the Vernier calliper.

Least count of Vernier calliper = 1mm/10 divisions=0.1 mm

A Vernier Calliper has a variety of applications.

Vernier callipers are instruments that are used to measure the length of a pipe or any other object of interest. The diameter of a spherical ball can also be measured with the aid of these instruments. In addition to a calliper, it is possible to measure the internal and external diameters of a hollow cylinder.

Screw gauge

When we turn the screw handle on a screw gauge, we get the linear rotation of the main scale that we need to record. This linear flow is used to determine the diameter of the wire or the thickness of the metal layer being measured.

When the anvil and spindle ends come into contact with each other, it is common for the zero mark of the circular scale to not correspond to the baseline of the main scale as a result of mechanical flaws. In either scenario, it is either above or below the main scale’s baseline, and in either case, it is claimed that the screw gauge has a zero error.

The basic difference between the screw gauge and the vernier calliper is that the screw gauge is only used for exterior measures, whereas the vernier calliper can be used for both external and internal measurements. The least count for the vernier calliper is 0.1 mm, whereas the least count for the screw gauge is 0.001 mm.

Least count of Screw gauge = 0.01 mm

Conclusion

The accuracy of an instrument is proportional to its least count value; this simply implies that an instrument that can measure smaller changes in a value than another instrument has a smaller least count value and is thus more precise.