More testing RD 1000    Robert Leverett    Aug 15, 2005 06:36 PDT  ENTS:    This past weekend saw my partner Monica Jakuc and I in Thetford, VT. staying with dear friends in a truly rustic setting. I had all my measuring equipment with me, but alas, there isn't a single tree in the region that merits measuring. Not one. So what did I do? Well, I homed in on our friend's outhouse and measured a horizontal 2 x 4 that was exactly 60 inches long. Yes, my weekend's big tree fortunes fell so far that I was forced to measure an outhouse. I can imagine some of your chuckles and under the breath comments. You measured what, Bob? No _ _ _ _.    Well, I set up a tripod at 132.5 feet away and measured the 2" x 4" both with and without the magnifier of the RD 1000. I consistently got two sets of results. Without the magnifier, I got an average of 60.3 inches with a variance of about 0.1 inches and with the magnifier I got 63.2 inches with a variance of slightly more. The magnifier causes an error in the over category. I moved to another location and got similar results. At one point, I got 64" with the magnifier. To put it bluntly, that sucks pond water. Looks like Laser Tech has some design flaws in the RD 1000. So my latest conclusion is NOT to use the magnifier or at least test it thoroughly.    On the way back home, Monica and I stopped by the famous Sunderland Sycamore in Sunderland, MA. Using the RD 1000, I modeled the first 12.5 feet of the great tree. That takes me up to the explosion of big limbs. After mis-calculating the volume courtesy of punching the volume formula in wrong, I finally got it right. The trunk to the branching point contains about 660 cubic feet of volume. Based on what my eyes tell me, I think the volume for the whole tree is between 2,000 and 2,500 cubic feet. Getting the upper limbs is going to be a real challenge, but I think we can do it courtesy of the RD 1000.    I still stand in awe of Will and Jess's Smoky Mountain adventure. They get to measure great trees and I get to measure a rustic outhouse. What has gone wrong here?    With respect to Lee's ascendancy in the ranks of the world's leading forest ecologists, I for one, had no doubt that Lee is destined to be one of the very top performers. Congratulations to you Lee. Bob Robert T. Leverett Cofounder, Eastern Native Tree Society RE: More testing RD 1000    Don Bragg    Aug 15, 2005 07:07 PDT  Bob-- I have recently spoke with a LaserTech rep on the RD1000 and got a quick demo. He told me that there was a linear relationship between the diameter accuracy and distance, so that the +/-0.25 inch accuracy at 80 feet translated into +/-0.5 inches at 160 feet, and +/-0.75 inches at 240 feet, and so on. I would guess that the magnifier also serves to multiply the relative accuracy of the RD1000, perhaps by the power of the magnification itself. Thus, I would think that at 132.5 feet from the target, you could expect an unmagnified accuracy range of roughly +/-0.4 inches, and if magnified by a 2.4 power scope, this may mean an accuracy range of at least +/-1.0 inch. I am not entirely sure if this is exactly how it works, but it could explain some of the variation you are seeing. The rep also told me that the RD1000 needed to be specifically calibrated to use magnification, so I wonder if this is something you have done... Does the RD1000 self-calibrate to the 2.4X magnifier, or do you have to reset it manually? Don Bragg Re: More testing RD 1000    Paul Jost    Aug 15, 2005 08:57 PDT  Bob, The RD1000 diameter measurement is specified at 1/4" accuracy at up to 80'. Error should decline proportionally at longer distances. It sounds like the first measurements were on par but that the magnifier causes distortion. I would be concerned about the resolution of the LCD "caliper" and would wonder how much of an increment each LCD caliper bar covers and how it relates to the observed measurements... Paul Jost RE: More testing RD 1000    Robert Leverett    Aug 15, 2005 09:28 PDT  Paul:    For my next testing, I'll record the distance to target and the amount of incremental diameter showing up on the LED for each click of the button that expands/contracts the scale and report them in a spreadsheet. That way we can look at hard data. Maybe we can put our heads together and figure out how to compensate for the distortion. The magnification factor is 2.14, if I remember correctly.    When I ordered the instrument, my main concern was achieving a high accuracy for diameter measurements at the kinds of distances that we encounter. That requirement seems to me satisfied so long as I supply the distance and don't use the magnifier. Given the advertised capabilities of the instrument, that's giving up a lot, but at least I can use the instrument.     The tilt sensor definitely has problems. I have abandoned further use of it. Pity. Bob RE: More testing RD 1000    Paul Jost    Aug 15, 2005 11:26 PDT  Bob, They are probably sensing tilt with an accelerometer that has improper bandwidth. If you are using a tripod, don't let it dip or jolt when you loosen the mount prior to aiming it further up the tree. Slow and smooth changes in inclination might make the clinometer useful again if that is the problem. Also, accelerometer-based clinometers often need to be zeroed out or calibrated to level so verify if the RD1000 has a calibration routine. Digital carpenter levels based on the same technology often recommend daily recalibration before use. Paul Jost RE: More testing RD 1000    Robert Leverett    Aug 15, 2005 12:47 PDT  Paul:    Thanks for the suggestions. They do have a method for aligning the Tilt Sensor. I'll do the procedure this evening and see if any difference is made. It is a process that determines an offset to establish the level position similar to what I read in your explanation. Bob RE: More testing RD 1000    Robert Leverett    Aug 15, 2005 12:54 PDT  Don:    Thanks. The instructions that came with the unit said that no calibration of the magnifier was necessary if the magnifier that came with the unit was used. I obviously need to check to see if the magnification constant on the magnifier matches what is being used by the unit. I foolishly have not checked. I will do so. Based on the outhouse experiment, the error on a 132.5-foot baseline falls within the +/- 0.4 inches you mention without magnification. The error with magnification was a hefty 3 to 4 inches.    More tomorrow. Bob     RE: More testing RD 1000    Robert Leverett    Aug 16, 2005 05:30 PDT  Don and others:    I checked the magnification constant for the RD 1000 last evening. It was correct. I also went through the simple leveling procedure to calibrate the leveling offset. Both efforts were to no avail. I think we have some design deficiencies in the instrument.    I hope I can compute some kind of curve to use for the tilt sensor. That's next on the agenda. The same is true for the magnifier. I do like having the magnifier. I can see the edges of a tree trunk much better. Bob Home