Every industry has a jargon of its own and dimensional metrology is no different. The reason is ease of verbal communication, but that communication can be confusing at times for the uninitiated. For example, all measurement systems, whether they are old or new, have units of measurement that are ignored for all practical purposes. An example of this in precision engineering is where ‘inches’ prevail over ‘feet’ in the Imperial system. The metric system has similar orphans as well.
Awareness of the practicalities of both systems makes it easier to understand the evolution of the jargon so let’s take a look at both of them.