Leica DISTO classic User Manual page 33

Or:
Aim at third point.
Trigger measurement.
End function, the height and
distance are displayed from three
measurements (Pythagoras).
For short distances, a good base
behind the instrument is sufficient
for mechanical alignment.
After "2 ---", align the DISTO
approximately horizontally.
You will obtain the best results if
the DISTO is rotated around a
fixed point (rear edge, thread
position) and the axis of the laser
beam passes through this axis. So
do not simply place on a camera
tripod, in this case the axis of the
laser beam is approx. 70 to 100mm
above the centre of rotation, this
can lead to significant variations in
the height.
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