Metrology Through Ages

Abstract

Since time immemorial human beings have been weighing and measuring objects in one form or the other, and have been trying to define units of measurements. Normally one compares a quantity of a particular body with that of another body, whose quantity, under question, is known. In earlier days, one might have compared similar quantities, one of which could have been a part of the human body, for example the foot of a person. The problem with such definitions was encountered when this unit was to be implemented throughout the country. In this case, persons with different foot lengths would assign different numbers for a given distance. To obviate this difficulty they could have decided to estimate all distances in terms of the king’s foot length. However, the problem with this system would be that the king could not be expected to go wherever a distance needed to be measured, and the question of what would happen after his death too would arise.

The next bright idea was to use an artefact like a piece of wood, metal or some other material as a unit of length. One of the earlier records of such an artefact was found in the form of an “Egyptian Cubit” around 2,500 BC. This first welldocumented example was derived from the length of the arm from the elbow down to the outstretched tip of the middle finger. By 2,500 BC this had been standardised as a royal master cubit made of black marble (measuring about 52 cm). This cubit was divided into 28 equal parts (each roughly the width of a finger), which could be further divided into fractional parts, the smallest of these being just over a millimetre. About 500 years later a royal decree about length, weight and capacity measures was issued in Babylon. This was a piece of granite whose length was equal to the length of the forearm plus the width of the palm of the Pharaoh ruling at that time.