Abstract :
People who measure things - metrologists - are often unduly modest about their role in society. However, consider this: the wheel is lauded as the preeminent invention of stone-age man, although it is impossible to make a satisfactory example without a measuring-stick to ensure that all parts of the circumference are equidistant from the axle. Also, the progression of hunter-gatherer man to farmer man was facilitated by a clock whose indicating hand is the apparent motion of the sun across the sky, and even more by a calendar to set the optimum time for sowing seed, harvesting and so on, provided by the cyclic position of the rising or setting sun along the horizon. Therefore, all down the ages, advances in technology have usually been preceded by advances in measurement, even though occasionally, even within living memory, quite technically advanced machines were made on an individual basis without too much regard for metrology. I have in mind the engineer making steam locomotives who, when asked about machining tolerances, apocryphally replied, "We don\´t have tolerances - we make things fit!" Then Henry Ford came along, and, with the aid of accurate dimensional measurements, made interchangeable items and mass-production was born, except that it originated much, much earlier. More than two thousand years ago crossbows like those held by the soldiers of the Chinese terracotta army had trigger mechanisms to fire their bolts, which were cast in bronze from exact molds that made their parts interchangeable throughout the empire.
