"Paul Sengupta" wrote in message
...
"Tony Cox" wrote in message
ink.net...
Assuming the mode C is properly calibrated, that is.

How do you measure altitude at 328k feet? Surely a standard
barometric device isn't going to work?

Paul

Below about 50 milliBar, people use a Pirani Gauge, which is
essentially a broken light bulb -- the wire gets hotter &
changes electrical resistance as there is less air to cool the
wire. 50mBar is around 75K ft.

Lower than about 10-2 milliBar, Ion gauges are the way to
go. They are like broken vacuum tubes.