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# The Philosophy and Consequence of Measurement - Precision

We began our series of Blog postings to generate discussion and comment around scientific measurement by looking into the philosophy and consequence of measurement.

As the great scientist, Lord Kelvin, once said, ‘When you cannot measure… your knowledge is of a meagre and unsatisfactory kind’.

Now we continue into the need for test equipment by looking at 6Ps (Precision, Power, Performance)- (Productivity, Portability, Package) and begin with Precision.

1. the state or quality of being precise.

2. accuracy; exactness: to arrive at an estimate with precision.

3. mechanical or scientific exactness: a lens ground with precision.

4. punctiliousness; strictness: precision in one's business dealings.

5. Mathematics . the degree to which the correctness of a quantity is expressed.

Precision and Accuracy mean slightly different things!

- Accuracy is how close a measured value is to the actual (true) value.
- Precision is how close the measured values are to each other.

So, if you are throwing darts always hit 1 instead of treble twenty, then you are not accurate, but you are precise! Therefore a measurement system can be accurate but not precise, precise but not accurate, neither, or both.

For example, if an experiment contains a systematic error, then increasing the sample size generally increases precision but does not improve accuracy. The result would be a consistent yet inaccurate string of results from the flawed experiment. Eliminating the systematic error improves accuracy but does not change precision.

When we think of precision instrumentation we generally think of the most fundamental of measurements such as micrometers, callipers, precision levels, the plumb bob, laser distance meters, radius gages, microscopes (for surface finish inspection), feeler gages, electron microscopes, atomic clocks.

Precision then is all about transferring the variable from its source to the measurement device without distortion or interference or degradation so that measurement can be reproduced and repeated.

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