The Metre Rule
This instrument is commonly used in the laboratory to measure the length of wires or the distance between two points. Greater accuracy is attained by measuring from the 1.0 cm mark and then to subtract 1.0 cm from the result, because the zero mark is the end of the ruler is vulnerable to wear and tear.
For accurate measurement, the eye must always be placed vertically above the mark to avoid parallax errors.
Vernier Callipers
By means of a Vernier scale, the second decimal place in cm can be obtained without having to estimate fractions of a division using the eye. They have a set of inside jaws which can measure the internal diameters of tubes and containers.
Micrometer
A micrometer can be checked for any zero error, by turning the spindle until the anvil and spinner meet. The zero mark has to lie directly opposite the datum line of the main scale.