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The Philosophy and Consequence of Measurement – Accuracy


""‘When you cannot measure… your knowledge is of a meagre and unsatisfactory kind’. Lord Kelvin

We continue looking into the need and specifications for test equipment by looking at 6Ps (Precision, Power, Performance)- (Productivity, Portability, Package) and from Precision we look at the associated trait of Accuracy.

As previously described, precision and accuracy mean slightly different things! Precision is how close the measured values are to each other and accuracy is how close a measured value is to the actual (true) value.

Accuracy- the quality or state of being correct or precise: technical- the degree to which the result of a measurement, calculation, or specification conforms to the correct value or a standard.

When it comes to a standard and accuracy a good place to start is the atomic clock and the Hafele–Keating experiment to test the theory of relativity. In October 1971, Joseph C. Hafele, a physicist, and Richard E. Keating, an astronomer, took four caesium-beam atomic clocks aboard commercial airliners. They flew twice around the world, first eastward, then westward, and compared the clocks against others that remained at the United States Naval Observatory. When reunited, the three sets of clocks were found to disagree with one another, and their differences were consistent with the predictions of special and general relativity. Time travel?

From 1971 to last month; January 2014 and the announcement of a new strontium atomic clock built by American researchers which is reputed to be 50 per cent more precise than the previous record-holding device as described in a recent issue of The Journal Nature. The new strontium clock is accurate to within a second in about five billion years, which is more than the current age of the Earth. The previous record holder – NIST’s quantum logic clock was only 50 per cent that precise. The only competitor that can match the strontium precision is the NIST’s ytterbium clock, unveiled in August 2013. Besides being incredibly precise, the clock also offers an unprecedented level of stability.

From that example of precision and accuracy we’ll move on in our next article to look at precision, accuracy and stability of more commonly used test equipment.

Rejoice in your measurements. Demand more and enjoy this series.