Jerome, your right about my laser engraver and CNC router both are capable of either imperial or the metric system. However they are simple software configurations so there's no reason to be concerned with making a mistake. Even if I load a metric drawing the software automatically converts it to imperial dimensions, but that's unlikely to happen since I don't accept metric projects. I am fortunate that I am in a position to be able to bid or no-bid projects that don't fit my requirements. Currently I am basically semi-retired so I have even more flexibility concerning my shop schedule.
I can't remember any of the details but many years ago NASA had an incident where a metric dimension was misinterpreted as imperial and the lander missed a planet by a hundred miles. They were embarrassed about the incident but it was just taxpayers money so no big deal. If that happened to me in my little shop it would be devastating.
I spent half my life as a Quality Control Inspector and I have had my share of situations where a machine shop I was at to inspect a project before they could ship and found dimensional errors or even drawings that were not the current revisions. I've seen shop supervisors faces turn white as a ghost when I explained a problem I found and they instantly knew that they were in big financial trouble. I learned early in life how serious errors can be and when I opened my own shop I made certain decisions about basic policies I had to abide by to limit my own liability. Inspectors make a living based on the fact that people make mistakes, we had T-Shirts at North Anna Power Station in the late 70's that said "We Live By Your Mistakes". Sometimes they were billion dollar mistakes that made it crystal clear to the customer that inspection was worth every penny invested
There's nothing simple about any system of measurement, its more like a science than it is a directive in a specification. For instance there is a right way and a wrong way to use a simple micrometer, if you want to learn the right way find a Master Machinist and ask him to teach you how its done properly.
It really is about the money folks
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