Least count of an instrument is used to select the right instrument for your applications. For example if you are selecting an instrument to measure a dimension 6.2 ± 0.25 mm. You can not use a ruler. In this article we will discuss what is lease count and how to calculate it.
What is Least Count (L.C.) ?
Least Count of an instrument is the smallest measurement that can be taken using an instrument. In other words, it is the smallest change an instrument can measure. For example, using the ruler shown below we can measure a minimum 1 mm length. Therefore ruler L.C. is 1 mm.
Least Count vs Precision
L.C. is directly related to precision. If an instrument has a small L.C., that means it is more precise.
For example, if you compare digital and mechanical vernier caliper. Digital Vernier L.C. is 0.01 mm. Whereas mechanical vernier L.C. is 0.02 mm. Therefore digital vernier is more precise compared to mechanical vernier.
Least Count vs Accuracy
L.C. is the minimum dimension that can be measured using an instrument. Whereas Accuracy is how close a measured value is to actual value when that value is measured repeatedly. Read this article for more details on accuracy.
How to Calculate Least Count?
L.C. for an instrument is calculated by dividing main scale reading with number of divisions.
Main Scale L.C. = Smallest Reading on Main Scale / Number of Divisions
Instrument L.C. = Main Scale L.C. / Divisions in secondary Scale
Scale Least Count Calculations
Mechanical Vernier Caliper Least Count Calculations
Mechanical Micrometer Least Count Calculations
To sum up, the least count of an instrument is the minimum value that we can measure with an instrument. It is used in the selection of the right instrument for your application.
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