The meter scale is graduated at every millimeter. i.e., 1 m = 1000 mm

The minimum number of significant digits can be one (e.g., for measurements like 4 mm and 6 mm) and the maximum number of significant digits can be 4 (e.g., for measurements like 1000 mm). Hence, the number of significant digits may be 1, 2, 3 or 4.