Bob, it is my opinion that your new method for estimating trunk widths at various height intervals using the TP360 and "missing line" routine should in theory be more precise, faster and easier than using the Macroscope25 with laser. The Macroscopes are handy little items for estimating trunk width, but as you stated earlier, there is distortion when you fill the entire screen up on the Macroscope. There is just no way around this unless you can get trunk views that are far away which is difficult in a cluttered forest. I don't know how calculate this distortion error so I always try to get as far back as possible with the Macroscope25.
Also, just as significant may be the Macroscope25's 50 tick mark stadia scale which is cruder when compared to the TP360's .1 degree azimuth resolution. The accuracy relative to true North on the TP360 (which seems to drift a little from site to site and day to day) is not relavent to the accuracy of each trunk azimuth estimate from edge to edge. If I did my calculations correctly, each tick mark on the Macroscope is equivalent to .7625 degrees when using 75 as the Macroscope constant. This is lousy resolution when compared to the TP360. The key is for the Macroscope user to estimate in-between ticks. Can be done with practice but to .1 resolution like the TP360 ? Seems easier said than done.
Now the price tag of $1,600 for TP360 vs. $150 for Macroscope25 is a consideration for most people. A home-built horizontal transit is one cheaper alternative.
Wendell Flint measured the volumes of the giant sequoias for his book "To Find The Larges Tree", using a transit and horizontal sweep angles to determine trunk widths at various height intervals. His transit/tape-line derived trunk diameters have been proven very close to tape wraps and certainly more accurate than a Macroscope25 based measurement.
Bob, your new trunk diameter measuring technique is very practical and I would say accurate too. Thanks for posting your method on the NTS blog. I plan to use your method as soon as I get my hands on a TP360. I will use the remote trigger + tripod to get the best possible results from the TP360.
I may in fact ditch the Macroscope25 if the TP360 works better for me. Your results are very encouraging.
California AFA Big Trees Coordinatorhttp://www.landmarktrees.net