Above 18K feet, everybody is on pressure altitude. Down in the sewers, where
I fly, we're all on local pressure.

mike

"Mxsmanic" wrote in message
...

Not true. Altimeters show substantial differences with geometric
altitude as altitude increases. Air traffic control is based on
pressure altitudes, not geometric altitudes.

The altimeter is much more accurate.

That's what I would assume with my particular GPS.