Electronic and Physical Standards
The following list illustrates various limits of measurement and accuracy encountered in all areas of employment inside and outside Metrology. For any particular area, limits of accuracy are for comparison to Absolute Standards. Relative accuracies for each of the following areas are generally higher (in resolution).
For those who don't quite follow the shorthand table above, here is a simpler explanation of Metrology. A Metrologist is an engineer trained to design and conduct measurements to the highest degree of accuracy and resolution achievable. Please note that resolution is not a guarantee of accuracy. To say that someone can measure the distance of one foot covers a lot of ground. That is: is that 1 foot distance the same length as others would measure? To be accurate the engineer would be forced to say instead that they had measured one foot within one inch… but this is not very accurate. The National Institutes for Science and Technologies maintains a copy of a ruler that is known to be an exact length. This ruler is used to measure and compare other rulers and each of these rulers thus attains a known accuracy (by direct comparison to the primary standard). If an engineer can say that the distance measured was 1 foot when they used one of these rulers (which are properly described as a secondary standard); then they can also express my limits of accuracy. So from the table above, you may observe that when that engineer measures up to 1 foot in distance that these limits of accuracy would force them to add (for the sake of accuracy) that the distance falls between 11.99999 inches and 12.00001 inches. Further in saying that they used a ruler that was compared to a known standard (the primary standard), they are also performing a measurement that is traceable and this distinction carries some legal weight with it. For further discussion consult Metrology. |