From: "Bruce Gray" <Bruce@glasair.org>

My Smart Level, purchased in 1991, has the alternate zero. The normal
calibration process is to press the reset button for the first angle
setting then rotate the level 180 degrees and press the reset button for
the second angle setting. The Smart Level averages the 2 angles and sets
the average as level. To set an alternate zero you just put the smart
level where you want zero to be and press the reset button 2 times for
angle one and angle two. Zero is now the new preset angle.

Bruce
Glasair III
www.glasair.org