Re: [CAD_CAM_EDM_DRO] Conversion

James Owens wrote:

> Hi,
>
> I'm working on a DRO and am having some confusion over the conversion of
> metric units to inches and back again. The device should be able to read
> glass scales down to 0.001mm or 1 micron so it is important to get this
> right.
>
> I have always used 1" = 25.4 mm but on trying to work it out with a little
> more accuracy I find that an English mile = 1.609 kilometres or 1" =
> 25.39457071 mm. but this figure changes depending on who it is coming from.
>
> Does the list have any opinions on this.

EMC uses the conversion factor 0.03937007874016, which is the dimension
of a mm in inches. (Or, multiply by 1000 and you get the size of a meter,
which is 39.37.... inches.) Since this software was written by NIST, it is
essentially a "tracable standard", as they ought to be THE authority!

FORGET those miles, trying to convert inches to mm through miles is going
to get you in big trouble, I'm sure. Us common folk almost certainly have no
idea exactly how many inches or feet are in a statute mile. Land surveyors
probably are taught that in school, depending on how messy it really is, I
don;t know whether they remember it or not. (In practical terms, they can't
really use it, anyway, as everything is goofed up by the earth's curvature.)

Jon