In an experiment, a set of reading are obtained as follows - 1.24 ~mm , 1.25 ~mm , 1.23 ~mm , 1.21 mm. The expected least count of the instrument used in recording these readings is _ _ _ _ mm.

Step-by-step solution

Least count is the smallest division readable on an instrument scale. Given readings are 1.24 mm, 1.25 mm, 1.23 mm, 1.21 mm, all expressed to two decimal places. The precision of measurement shows differences as small as 0.01 mm (e.g., 1.25 - 1.24 = 0.01 mm). This indicates all readings can be recorded to the nearest 0.01 mm, which represents the smallest measurable division. Therefore, the least count of the instrument is 0.01 mm.