### Least Count of measuring instruments

In this article, we are going to learn about least count of various instruments and calculation of least count for measuring instruments. Following content is covered in this post.

**Content**

**What is least count?**

- Least count Vs Precision
- Least count Vs Accuracy

**Least count of various**

instruments

instruments

- Least count of Vernier caliper
- How to calculate least count of manual vernier caliper?
- Least count of Micrometer
- Micrometer least count calculation
- Vernier micrometer least count calculation
- Steel Scale least count
- Bevel protector least count
- Bevel protector least count calculation
- Least count of Dial Gauge
- Dial gauge least count calculation

**Least count of CMM, VMM**

**Least count of Contour**

machine

Difference between Varnier

caliper & micrometer

machine

Difference between Varnier

caliper & micrometer

**What is least count?**

It is smallest measurable value of any measurement

instrument. For example steel scale can measure 1mm, so least count is 1.0

Least count of an

instrument has direct relation with precision and accuracy of that measuring

instrument.

** Precision**–

It talks about how close is the measurement of same item to each other.

** Accuracy**–

It refers how close measurement of an item to its true value is.

**Least count vs Precision**

Least count is inversely proportional to precision.

Mean smaller least count; more will be its precision.

**Least count Vs Accuracy**

Least count is inversely proportional to accuracy.

Lower the least count more will be accuracy. Accuracy means measurement close

to true value. For example- 4.0 mm is true value; I am using Digital vernier

caliper to measure this dimension. My results are 4.002 but not 4.000. Here I

am 0.002 mm far away from true value (Which is instrument accuracy level) and

least count is 0.01 mm. So accuracy will be always less than least count of any

instrument.

Let’s understand with an example. We have mechanical

vernier caliper and Digital vernier caliper. Least count of mechanical vernier

caliper is more than digital vernier caliper. If I measure any dimension with

mechanical vernier caliper, then result of that dimension will not come same

each time, there will be variation each time.

But if I check same dimension with digital vernier

caliper, then we will get same value of that dimension on each measurement.

That is precision.

So digital vernier caliper is more precise as compared

to mechanical vernier caliper. It is because digital V.C has low least count.

**Least count of various instruments**

Instruments used in industries for measurement are- Vernier caliper, Micrometer, Profile Projector, Dial gauge, Bevel protector, CMM, VMM, Hardness Tester, Roughness Tester, contour machine, Rapid Eye, Height Gauge, etc. Each instruments has its least count and there is calculation for least count of various instruments, which is explained below.

All measuring instruments with Least count |

**Least count of Vernier Caliper**

There 2 types of vernier caliper. Type 1 Mechanical

vernier caliper (Also called Manual vernier caliper) and Type 2 is digital

micrometer. Least of both type of vernier caliper is different, which is

explained below.

Least count of Manual Vernier caliper= 0.02 mm

Least count of Digital Vernier Caliper= 0.01 mm

Vernier caliper types and Least count |

**Manual vernier least count calculation**

In mechanical vernier caliper, there are 2 scales (Main

scale and another one vernier scale) so we have to calculate least count of

both scale.

First calculate least count of main scale– Smallest reading

on main scale/No of division on main scale. Here 1cm/10 Division=0.1 cm

Now calculate least count of vernier scale- Least count

of Main scale/No of division in vernier scale. Here 0.1/50=0.002 cm, if we

convert to mm, it will be 0.02mm.

Refer below picture for more understanding.

Least count calculation of vernier caliper |

**Least count of Micrometer**

There are different types of micrometers like- outside

micrometer (or screw gauge), digital micrometer, Vernier micrometer, etc. Least

count of these micrometers is different, which is explained below.

Least count of Outside Micrometer= 0.01 mm (10 micron)

Least count of Vernier Micrometer= 0.001 mm (1 micron)

Least count of Digital Micrometer= 0.001 mm (1 micron)

Micrometer Types and Least count |

**Micrometer least count calculation**

Before going direct on calculation of least count of

micrometer, first understand it important parts like- Main scale division, main

sub division and thimble scale.

Now for least count of any instrument we have to found

smallest measurable unit of that instrument, then divide that unit by its

numbers of divisions.

Here in micrometer, we have main scale which is divided

into 2 parts- Main scale (Upside) and Main Sub division (Downside). On main

scale we can measure 1 mm and on rotation of thimble division by one round,

0.5mm measurement is completed on main sub division (It means I have to rotate

thimble division by 2 round to complete 1 mm). Here 0.5 is least count of main

scale and total divisions on thimble scale are 50. Then least count will be

0.5/50= 0.01 mm.

Refer below picture for more understanding.

Least count calculation for Micrometer |

** **

**Vernier micrometer least count calculation**

To write measurement result of vernier caliper, we have

to write in 3 decimal places. Because least count of vernier micrometer is 1

micron (0.001 mm).

In micrometer, the reading is accomplished by adding

the whole millimeter, the half millimeter, and hundredth of millimeter just as

we do in outsite micrometer (Simple micrometer). But in vernier micrometer, we

have to add the number of 1 thousandth of millimeter. See below picture for

better understanding.

Vernier caliper least count calculation |

**Steel Scale /Measuring tape least count**

Steel scale can measure 1 mm minimum. So least count of

steel scale is 1mm. Same least count is applicable for measuring tape.

**Bevel protector Least count**

Bevel protector least count is 5 minute (5’). Bevel

protector is used for angular measurement. Range of bevel protector is 360˚.

**Bevel protector least count**

calculation

calculation

Formula for least count calculation of vernier bevel

protector is division of least count of main scale division by total number of

division on vernier scale). In bevel protector least count for main scale is 1˚

or 1 minute and total divisions on vernier scale are 12 (Left side & Right

side). On converting calculation (1/12×60) in minute we get 5 minute.

For more understanding about least count of bevel

protector refer below picture.

Bevel Protector Least count calculation |

** **

**Least count of Dial Gauge**

Least

count of dial gauge is 0.01 mm. Because 1 revolution of large hand indicator is

equal to 1 mm movement. It is used to measure small distance from range of 5mm

to 10 mm approx. Dial gauge or Dial indicator is device used to measure angle,

concentricity, flatness, straightness of any object. Dial gauge come with

different types depends its application.

**Dial gauge least count calculation**

Least count calculation for dial gauge is simple. Here

in dial gauge we see two scales. One is large scale contain 100 division. Small

scale containing around 10 divisions. 1 division in small scale is equal to 1

mm. So one revolution of large scale is equal to 1 division movement of small

scale. Formula for least count will be smallest measurement of small scale divide

by total number of division on large scale. Here 1 mm divided by 100 comes

0.01mm. This is least count. Refer below picture for more understanding.

Dial gauge with least count calculation |

**Least count of CMM & VMM**

CMM stand for coordinate measuring machine. It work on

pressure and its accuracy level is very high. As we know accuracy is inversely

proportional to least count. Since accuracy high then least count will be very

low. CMM can measure upto 1 micron. So least count is 0.001 mm.

**Least count of profile projector**

Profile projector least count is 0.001 mm ( 1 micron).

This is same as CMM.

**Least count of contour machine**

As we know least count is lowest possible measurement

of an instrument. There are various type of roughness tester which have

different capacity and range of measurement. But minimum measurement of

roughness is 0.5 micrometer by contour machine. So we can say least count of

contour machine is 0.5µm. But 0.1 micrometer is also possible with high

precision profile tester.

**Difference between Vernier caliper and Micrometer**

- Vernier caliper is used to

measure large dimension measurement(Length, Height) range upto 150 ~300 mm,

while Micrometer is used to measure small distance measurement (Dia,

Thickness). - Least count is different

for both instruments. - Micrometer is more precise

than vernier caliper. - Micrometer is costly

compare to Vernier caliper

This was all about least count of measuring instruments and their calculation method and Formula. Hope you found this post informative and useful. If you like follow me on below social media platform and also share with friends.