How to calculate least count in ammeter

how to calculate least count and why it is multiplied with the readings we get?

Any ammeter will have a range selector.

Suppose the range is selected as 0 to 300 mA.

Count the number of small divisions on the scale.

Suppose there are 30 divisions, then the least count is 300 /30 = 10 m.A

Least count means the smallest division that you can measure using that instrument.
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In an instrument a scale reads from zero to 20 A

From zero to 5 A there are 5 divisions .
Hence each division corresponds to 1 A
The least count of this ammeter is 1 A,
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Sorry - I don't understand. You need to explain what 'least count' is and maybe give an example.

Try posting a new question with this information included.