MEASUREMENT II.
Measuring length using vernier callipers.
Vernier callipers is used when higher accuracy in measurement is required and this cannot be done using a metre rule.
Vernier callipers has two scales; main scale and vernier scale. Outside jaws are used to measure both lengths and external diameters, inside jaws for measuring internal diameters while the tail is used for measuring depths of cavities .
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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.
MEASUREMENT.
In order to measure we need to know or define the quantity to be measured and the units for measuring it.
In 1971 a system known as the International System of Units (Systeme’ Internationale) and seven basic units were agreed upon as follows. Other quantities can be obtained from these basic quantities and are referred to as derived quantities.