Length is measured using the following instruments.
(a). Metre Rule: A metre rule is a measuring device calibrated in centimetres (cm) with a range of 0 – 100cm. In using the metre rule, the eye must be fixed vertically on the calibration to avoid parallax errors.The smallest reading that can be obtained on a metre rule is 0.1cm (0.01cm).
(b). Callipers:these are used in conjunction with metre rule for measuring diameter of tubes, thickness of sheet, etc. The callipers are of two types –
The external calliper and
The internal calliper.