wrote:

Lastly is a 100ft or 1000ft violation any different. it is still an
incursion either way you look at it.

No, it isn't. You can't ignore the accuracy of the measuring device.
For a glider with a cheap altimeter and a cheap GPS, 1-200 feet is well
within the possible measurement error at 18K. 1000 feet isn't (usually).

Read some of the stuff to do with RVSM.

The calibration of the logger and altimeter doesn't take into account
the position error when connected to the glider static source. Then
there are the gliders where the static source is just cockpit pressure.
Even if it's accurate in the test chamber, God knows what an altimeter
or logger will say when screwed in the glider.

Dick Johnson's reports always begin with calibration of the pitot-static
system and he has been scathing about the inaccuracy of some gliders -
mostly due to poor positioning of static sources. He's found errors of
7 knots in airspeed readings. Imagine what means for altimeter accuracy.

How is a pilot to KNOW that his logger is recording 18,200ft when his
altimeter says 17,900ft? On the OLC, YOU see what the logger said. The
pilot only knew what his altimeter said. When he lands, he has no
evidence that his altimeter never saw a violation.

These are gliders with no natural vibration. Next time you're climbing
through 17,500 feet, tap your altimeter. Ten bucks says it will jump
more than 100 feet if it's more than 5 minutes since your last tap. If
you get to 25,000, it'll jump nearly 200 feet.

Set your altimeter sub-scale to quarter of an inch above QNH, tap it,
then wind it back to QNH and read the altimeter without tapping. Do it
again but start from quarter of an inch below QNH. Even at near sea
level altitudes, many gliders will differ by 50-100ft AT THE SAME QNH!

You've got a lot more faith in cheap instruments than I have, Al.

GC