Re: [CAD_CAM_EDM_DRO] Slightly off-topic : History behind lettered drills

In a message dated 10/3/00 3:37:47 PM Pacific Daylight Time,
Ian@... writes:

<< Wasn't there some confusion between metric and
imperial units on a spacecraft somewhere? >>
There sure was! Caused a Mars explorer to crash on the surface of Mars. I
don't remember the details, but caused the landing rockets or something to
fire at three feet instead of three meters. Also, by law, the US is on the
metric or ISO system of units by act of congress, and the US inch is set at
25.4 mm. The confusing thing about the 12s system is that we use fractions
down to about 1/64 of an inch then jump to a decimal to measure 100s and
1000s of an inch. But, there is more than just units involved here. US
drawings for auxilery views are a different convention than UK scrap views.
That can be confusing no end. Here in the US there are four common gauges of
metal thickness (really a weight measure, not thickness) But in the final
result as long as you are consistant with your units you should come out OK.
BLESS THE PERSON WHO INVENTED THE CHEAP ELECTRONIC CALCULATOR!!!.
John Meacham
(At one time a member of the US metrification council)