OVERVIEW

Mass, density and dimensions are grouped together largely for convenience but there is an obvious link between them in that density can be derived from knowledge of mass and dimensions. Perhaps more significantly, they are all measurements which are used as an essential part of other physical tests. For example, density is used to calculate volume loss in an abrasion test or as an integral part of volume change measurements. There are very few methods that do not at some point involve the measurement of dimensions and for many tests mass is an essential parameter. Density and dimensions also have a certain link in the factory, both being important as regards the costing of products. Density is very commonly used as a simple but effective quality control check on batches of compounded rubber as a guard against gross errors; and dimensional checks on products are one of the common operations of routine inspection.

Hence, both in the laboratory and in the factory, density and dimensional measurement have a particular position due to their frequent usage. Measurements that are made every day have a habit of being taken for granted and this can certainly happen to the measurement of dimensions, resulting in unnecessary errors. When one considers that in, for example, the determination of tensile strength, any error in the measurement of the cross section results directly in an equivalent percentage error in the strength measurement, it is reasonable to devote considerable attention to the seemingly simple matter of measuring...