From: "Bruce McEwen" <silkeplsn@worldnet.att.net>

Charlie:

I think you're describing the same one that I have.  The calibration
procedure goes like this:

 - Set the level on a table and depress the calibrate button
 - Count to 10
 - Rotate the level 180 deg and depress the calibrate button again
 - wait until the display gives you a measurement and you're done

Note that the surface that you use does not have to be level, but you do
want to be sure that you're fairly accurate in rotating it 180 deg to
ensure proper calibration.

Bruce McEwen & Silke Paulsen
Super ES
Chapter 7, the wings