The meter rule:

A meter rule is a length measuring instrument as shown in the figure. It is commonly used in laboratories to measure the length of an object or the distance between two points. It is one meter long which is equal to 100 centimeters. Each centimeter (cm) is divided into 10 small divisions called millimeters (mm). Thus, one millimeter is the smallest reading that can be taken using a meter rule and is called its least count.

Least count of meter rule = 0.1 cm or 1mm