Introduction. Basic concepts and definitions. Measurement, the measurement result, measurement errors and their classification, the accuracy of the measurement
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Introduction. Basic concepts and definitions. Measurement, the measurement result, measurement errors and their classification, the accuracy of the measurement.
The death penalty faced those who forgot or neglected their duty to calibrate the standard unit of length at each full moon. Such was the peril courted by the royal site architects responsible for building the temples and pyramids of the Pharaohs in ancient Egypt, 3000 years BC. The first royal cubit was defined as the length of the forearm from elbow to tip of the extended middle finger of the ruling Pharaoh, plus the width of his hand. The original measurement was transferred to and carved in black granite. The workers at the building sites were given copies in granite or wood and it was the responsibility of the architects to maintain them. Even though we feel ourselves to be a long way from this starting point, both in distance and in time, people have placed great emphasis on correct measurements ever since. Closer to our time, in 1799 in Paris, the Metric System was created by the deposition of two platinum standards representing the metre and the kilogram – the forerunner of the present International System of Units – the SI system.In the Europe of today we measure and weigh at a cost equivalent to 6% of our combined GNP, so metrology has become a natural and vital part of our everyday life: Coffee and planks of wood are both bought by weight or size; water, electricity and heat are metered, and that affects our private economies. Bathroom scales affect our humour – as do police speed traps and the possible financial consequences. The quantity of active substances in medicine, blood sample measurements, and the effect of the surgeon’s laser must also be precise if patients’ health is not to be jeopardised. We find it almost impossible to describe anything without referring to weights and measures: Hours of sunshine, chest measurements, alcohol percentages, weights of letters, room temperatures, tyre pressures ... and so on. Just for fun, try holding a conversation without using words that refer to weights or measures. Then there is commerce, trade and regulation that are just as dependent on weights and measures. The pilot carefully observes his altitude, course, fuel consumption and speed, the food inspectorate measures bacteria content, maritime authorities measure buoyancy, companies purchase raw materials by weights and measures, and specify their products using the same units. Processes are regulated and alarms are set off because of measurements. Systematic measurement with known degrees of uncertainty is one of the foundations of industrial quality control and, generally speaking, in most modern industries the costs bound up in taking measurements constitute 10-15% of production costs. Good measurements can however significantly increase the value, effectiveness and quality of a product. Finally, science is completely dependent on measurement. Geologists measure shock waves when the gigantic forces behind earthquakes make themselves felt, astronomers patiently measure the dim light from distant stars in order to determine their age, atomic physicists wave their hands in the air when by making measurements in millionths of a second they are able at last to confirm the presence of an almost infinitesimally small particle. The availability of measuring equipment and the ability to use it effectively are essential if scientists are to be able to objectively document the results they achieve. The science of measurement – metrology – is probably the oldest science in the world and knowledge of how it is applied is a fundamental necessity in practically all science- based professions.
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