Laser Rangefinder Calibration   Edward Frank
  Dec 15, 2005 18:37 PST 
Will, Bob, Jess, ENTS

In Will's Tree Measuring Guidelines he talks about calibrating the
laser rangefinder - essentially determining the true distances at
various clickover points. It would be useful to expand upon the
discussion, including definitions of click-over, the differences between
Accuracy and Precision, especially for newer members considering buying
laser rangefinders. The explanation is excellent, but I would like to
post something to the website dealing with just this aspect of
calibration to go with the clinometer calibration post I sent in
September. Including just this explanation as a stand alone excerpt is
another option.

Will Wrote:

General questions
· The laser only reads in .5 to 1 yard (or meter) increments, how can it
be so accurate?

Before you use a new laser, it must be calibrated. To do this, stretch
out a long measuring tape flat on the ground. Have an assistant stand at
various locations on the tape with a reflective target. Place yourself
in a position so the eyepiece of the laser is over the “0” mark on the
tape. Alternately, you can do this by yourself by affixing the “0” end
to a reflective target and walking down the tape, shooting back at the
target and noting your position at click-over. Shoot a known distance;
say to 40 yards (or meters). Have the assistant move the target closer
or away from you until you get to the “click-over”, or inflection point
of the laser for 40 yards (or meters). Note where the target is in
relation to the tape. Do this calibration over a wide range of distances
to see the variation and correction factor to use (if needed). For
example, if the laser reads 40 yards at a distance of 40.6 yards based
on the measuring tape, then you would use that figure when your laser
gives the click-over reading for 40 yards. By calibrating your laser,
you can actually be mere inches off in the distance measuring part of
the tree height.

Edward Frank