Date: Wed, 14 Sep 2005 14:06:28 -0400
From: "Leverett, Bob"
Bob, Don, Ed, and others,
I thought it might be good to summarize the test results to date that I've conducted on the RD 1000 and to lay out what I think needs to be done.
First of all, I like the instrument and its feel in my hand. The strap attachment to hang the RD 1000 around my neck is a pain in the neck. It gets in the way, but I can detach the instrument from the strap and all is well.
So far my tests show that at or near eye level and for distances of 50 to 80 feet from the target, the RD 1000 works well for targets in the range of 20 to 40 inches in diameter when the instrument is used in continuous scale mode. Additional tests with gap mode need to be performed. Oddly, at a particular distance and for a particular target, switching from continuous mode or gap mode or vice versa, slightly changes the diameter reading. Same target, same distance, different interpretation. Hmmm. On the tests I've performed thus far, the gap mode reading is in the direction of too much. That is contrary to suggestions in the instructions that suggests better results can usually be obtained using the gap mode in the diameter routine. They did hedge their bets.
For long distances and narrow targets or short distances and wide targets, the scale reaches limits of contraction or expansions. One set of future tests will be to identify where these limits occur so that the user doesn't get set up at what appears to be an ideal location only to find that the scale cannot be expanded or shrunk to match the target's width.
The series of readings one gets at a particular distance by expanding or contracting the scale is a set pattern and each reading is at a fixed increment/decrement from the last with a 0.1 inch added/subtracted here and there, so that clicking the scale expander/contractor leads to a predictable result. This initially came as a surprise to me. I then understood that the scale is graduated in increments that depend on the distance from the target.
With distances from instrument to target of more than 95 feet, the width of the scale that best matches the trunk seems to overstate the diameter by one click going to two at distances of 125 feet. At distances from the trunk of under 50 feet, the pattern is unclear. From one test, it appeared that at lesser
distances than 95 feet, the best fit image overstated the diameter by 1 click, but I haven't gotten consistent results in the under 95-feet distance range.
Bob, as you suggested in an e-mail, I need to experiment with round objects, so I can know very accurately what the actual diameter is to compare with RD 1000 readings. I guess I'm going to need to buy some really big garbage cans or find acceptable substitutes.
I intend to do more tests with the tilt sensor. Early tests were performed at close distances where I may have introduced errors with where I had my eye and the tilt of the instrument relative to the tilt of my own head. At very close distances, the error introduced by the observer can be larger, apparently much larger. I could draw the triangles and make calculations, but suffice it to say that shooting the wall on the opposite side of my dining room may have pushed the envelope too far. However, yesterday's height measurement of the broken-topped Dunbar Brook hemlock using the RD 1000's tilt sensor versus clinometer and laser rangefinder was very satisfying (118 versus 117.1 feet).
The timely completion of future tests will depend on my time, of course, but I'm determined to give this instrument a thorough scrub down and will dutifully report all results. I regret that the tests are now having to be done piecemeal, but that's currently all my time will allow.
Bob
|