The at Home Mechanics Guide to Precision Measuring

The world of measuring is so complex by nature that one could get wrapped up writing an entire book on the subject and still not cover it all. This is not my intention with this book. My aim is to provide you with the principles of how measuring works, what the most important takeaways are on the subject of measuring, and an overview of how to use the tools correctly. Once informed you can then delve further into the intricacies of measuring depending on your own needs.

There are three terms which are important to the fundamental understanding of measurement. These terms are often mixed up, confused as meaning the same things, or used incorrectly. These terms are accuracy, precision, and resolution. Understanding these three terms will go a long way in ultimately understanding measuring and the capabilities of individual measurement tools.

ACCURACY
Accuracy is how close a given measurement is to the “true” value of an object. For example, if a valve stem was exactly 0.1969” (5.000mm), accuracy would quantify how close the measurement tool was to the true value.
PRECISION
Precision is a measurement of repeatability. For example if an object was measured five times, precision would quantify how close the five measurements are to one another. Another way to think of precision is the finiteness of which a measurement tool can be read repeatedly and reliably.
RESOLUTION
Resolution is the smallest distinguishable value of a measurement tool. An example being if a ruler is divided up into tenths of an inch then the resolution of the ruler is one tenth of an inch. A micrometer that can be read to one ten thousandth has a resolution of one ten thousandths of an inch. Just because a measurement tool, such as a micrometer, has a very fine resolution doesn’t mean it will be accurate or precise to that resolution. This will be explained in depth further into this chapter .