> Olin Lathrop wrote:
>> Sean Breheny wrote:
>> > In other words, the calibration method will probably have
>> > to involve multiple known distances at several frequencies, AND this
>> > will all probably shift with temperature.
>>
>> And pressure and to a lesser extent humidity, basically anything that
>> effects the speed of sound in air.
>
> And these calibrations will have to be done to insane levels of precision.
> Assuming the span in question is on the order of, say, 10", 0.0001"
> accuracy will require knowing the speed of sound under all conditions to
> better than 10 PPM. And, of course, the air in question will have to be
> perfectly still. Basically impossible.

*snicker* What if he's doing it in a vacuum?

Mike H.

(In all seriousness, what about a known environment, like 10PSI
pure nitrogen?)
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