At 08:59 PM 12/15/1999 -0500, you wrote:
>At 19:03 12/14/99 , t obrien wrote:
>>>The silliest thing of all is that the US still does not use metric.
>>Excusse meee....
>>We do use metric...
>
>It's been pointed out that .001 inch is about the limit of machining
>accuracy, and .0001 inch is about the limit of grinding accuracy -- this
>makes inches a very convenient unit in the machinist's world.  Millimeters
>are much less convenient in this instance.
>
>David Beierl - Providence, RI

Most CNC machine tools are built as metric machines, w/ inches & required
algorithms thrown into the software, & the smallest increment that is
programmable is .0001 inches (one tenth of one thousandth of an inch):
however the machines will accept .001 mm as a metric least increment, which
works out to ~.00004 inches, or 4 tenths of 1 tenth of a thousandth of an
inch!! i.e., in metric mode the tools are more than twice as accurate!

FWIW:  a human hair measures ~.003" in diameter - 3 one-thousandths of an
inch.  There exists a penultimate unit of measure that made it's way down
from NACA in the old days known as RCH - ostensibly the finest unit of
measure ever detected, but which I can't divulge in a public/family forum
(let yer polluted imaginations run wild,  & the context is that in the old
Apollo days it was definitely a man's world, that going into space business!).

Austin