What is least count error?

It is an instrumental or random error related with the precision, i.e. limit are resolution of a measuring instrument. The smallest division on the scale of a measuring instrument is called its least count as measuring instrument may give different least counts in different measurements. The approximation made by an observer when the object falls within the smallest division of the scale also leads to this type of error e.g., a line AB is to be measured with a metre scale. Its one end coincides with zero and the other end falls within 2.5 and 2.6 cm, so an approximation has to be made about the length of the line say 2.55 cm.