If we are interested in measuring the size of a body accurately, we require measuring the length of the body first. To do that, we can use an ordinary scale whose least count is 1mm. if you want to measure length more accurately, then this; the least count has to be smaller. Such small length, including diameters and thicknesses, can be measured as fractions of a millimeter with the help of suitably mechanical devices. The most commonly used mechanical devices are venire calipers and screw gauge.
