RD 1000 stuff and a surprise   Robert Leverett
  Sep 30, 2005 12:51 PDT 

ENTS:

     Yesterday PM, I tried the magnifier on the RD 1000 again. Maybe I
thought that time would cure its ailment. I chose the Silver Maple in my
yard as the target. At 4.6 feet above its base, the tree measures 32.2
inches in diameter by the D-tape method. I have orange flagging around
the trunk at this height. The reading from the RD 1000 was 35.0 inches
at 66 feet level distance from the trunk and 34.8 at 96 feet away. BTW,
the 34.8 value is what reads on the scale. Readings above and below the
34.8 would have been 33.6 and 36.0. It is all through built in internal
tables. Consequently, there is no way to get a reading that exactly
matches the measured diameter, even allowing for a tiny amount of off
circular shape.

    The magnifier produced a scale reading that is high by 2.5 inches at
96 feet and 2.7 inches at 66 feet. I am hoping that the magnifier will
produce scale readings that are off by a predictable amount, but I'm not
counting on it. The magnifier is nice to use. It definitely improves
visibility, but accuracy goes to hell in a hand basket.

      I'm beginning to think that the RD 1000 was rushed to production a
bit too soon. The internal scales appear to have been constructed with
too many compromises taken and presently I can't figure out what those
compromises are. As for my personal use of the RD 1000, I am fairly
confident that I can make it a useful tool for volume measuring, but
only after completing many tests and developing an extensive calibration
chart will I become efficient. At present, I am reasonably satisfied
with the instrument at distances of 60 to 100 feet without the magnifier
and at elevations 20 feet below to 20 feet above eye level, maybe a
little wider range, but not much. At greater distances and steep angles,
a lot more work must be done.

Bob