Are You Confused About Measurement Terminology?

You do not have to be. There are a few key terms and once you understand these you are ready to talk about a wide variety of measuring devices. The important terms include; range, sensitivity, resolution, precision, repeatability, accuracy and reliability. These terms and definitions apply to measuring temperature, distance, pressure, magnetic fields, weight – just about everything you can measure quantitatively. Let’s start with range. This is the difference between the lowest and the highest measurement that the device or instrument can measure. For example, consider your bathroom scale with a range of 300 pounds. From near zero to 300 pounds it will provide readings – outside that range the scale is unreliable or might even break.

Sensitivity is also known as resolution and these are the smallest increment of measurement that a measuring device can detect. For example your bathroom scale might show weight in tenths of a pound so we would say this scale has a sensitivity of 0.1 pound.

Precision and repeatability are two terms that are used interchangeably to describe the consistency of a measurement. Note, that we did not say “accuracy”, we’ll talk about this in a moment. Precision is the ability of a measuring system to provide the same reading value for multiple measurements of the same parameter in the same conditions. This measurement of consistency does not however indicate the measuring values are true, accurate or reliable. Let’s go back to your bathroom scale example; if you step on and off the scale 15 times, do you get the same reading every time? Your precision and repeatability are good if you get the same value over and over.

And finally there is accuracy which is also occasionally referred to as reliability. Accuracy is the ability of a measuring device to not only have good precision and repeatability but also for the values to be correct to some known and accepted standard. Using our bathroom scale example, let’s say you truly weigh 180 pounds but every time you step onto your bathroom scale the reading says 187 pounds. The precision of your scale is good because you get the same reading each time but the accuracy is off by 7 pounds.

Typically, a measuring instrument is designed with a specific range, sensitivity and resolution and these do not change. Calibration is used to adjust the measuring output for optimal precision, repeatability, accuracy and reliability over the range of the instrument.

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