The attached spreadsheet speaks for itself. It contains the most comprehensive accuracy test to date that I have made of the diameter routine of the RD 1000. But first to explain the columns in the spreadsheet. The zero column reflects my preferred readings where I attempted to just cover the trunk with the diameter scale at the indicated distance, i.e. the zero column reflects my best fit. The adjacent columns (-3, -2, -1, 1, 2, 3) reflect me then shrinking or expanding the diamter scale one click at a time on the instrument and recording the indicated diameter. For instance, if I am at 60 feet from the trunk, shooting to a spot on the trunk 4.5 feet up that has a taped diameter of 32.3 inches (I put orange flagging around teh tree at the spot), the sequence of values I get with the RD 1000, by contracting/ expanding the scale, is .....31.1, 31.8, 32.5, 33.3, 34.0, 34.7, 35.4.... . If my eyes fail me, or the instrument does, and I don't select the 32.5 reading, as I click the trigger to get each reading, you can see that I'll be off by 0.5 inches from the taped diameter if I choose 31.8, or off by 1.0 inches if I choose 33.3.
There were instances in my test where the scale was obviously too wide or narrow at the closest reading to the taped diameter from the sequence based on the distance from the spot. Had I not taped the tree, and I chose to take a single reading, what appeared to be the best fit, I would have no way of knowing that what clearly looked to be the best fit actually wasn't and that the reading reflecting the best fit didn't appear so in the viewfinder, i.e. the scale was clearly wider or narrower than the trunk at the spot.
At this point my conclusion is that the RD 1000 is a useful tool for ENTS purposes, but it has definition limitations based on how the diameter scale works internally. As a bit of added explanation, please note that in the spreadsheet, column J is entitled "Scale". Cell entries carry either a C or G. C is for the continuous scale mode that is used to mask the trunk with the red, highlighted scale. G is for the gap-scale mode that is used to fit the trunk into a gap with the red highlighted scale on the left and right sides of the trunk, i.e. the trunk fits into a gap in the scale. With clicks, you expand or shrink the gap. I was surprised to see that at the exact same spot on the trunk, when I switched from C to G slight changes the diameter reading occurred - an anomalie. I suspect the developers are well aware of the feature and chose not to advertise the anomalie. They must know that they have a slight design flaw. Please remember that the instrument is not seeing the trunk, merely doing internal calculations based on a distance fed to the RD 1000.
My next experiment will be to test the RD 1000 for a smaller diameter tree (around 24 inches), followed by a larger diameter tree (around 44). At this point I can well imagine users of the instrument walking around the woods taking quick fixes and moving on, confident that the accuracy claims for the instrument protect them. For forestry work, the averages may work out pretty well, as evidenced by column N in the spreadsheet, but for ENTS, which models individual trees, one heck of a lot of readings and plenty of analysis of the patterns is going to be required. However, I smugly predict that we will become THE experts in the use of this instrument.
| RD 1000 | Clicks ---------------------------------------------------------> | |||||||||||||
| Distance- ft | -3 | -2 | -1 | 0 | 1 | 2 | 3 | Avg Interval between clicks | Scale | Difference of actual from taped | Pct diff | Difference of best potential from taped | Pct diff from best potential reading | |
| 40 | 34.0 | C | 1.7 | 5.3% | ||||||||||
| 40 | 34.1 | G | 1.8 | 5.6% | ||||||||||
| 45 | 32.9 | C | 0.6 | 1.9% | ||||||||||
| 50 | 31.2 | 31.8 | 32.4 | 33.0 | 33.6 | 34.2 | 34.8 | 0.6 | C | 0.7 | 2.2% | 0.1 | 0.3% | |
| 56 | 33.9 | G | 1.6 | 5.0% | ||||||||||
| 56 | 33.1 | C | 0.8 | 2.5% | ||||||||||
| 60 | 31.1 | 31.8 | 32.5 | 33.3 | 34.0 | 34.7 | 35.4 | 0.7 | C | 1.0 | 3.1% | 0.2 | 0.6% | |
| 66 | 31.1 | 32.0 | 32.7 | C | -0.3 | -0.9% | -0.3 | -0.9% | ||||||
| 66 | 32.1 | G | -0.2 | -0.6% | ||||||||||
| 66 | 32.7 | C | 0.4 | 1.2% | ||||||||||
| 66 | 32.9 | G | 0.6 | 1.9% | ||||||||||
| 70 | 31.4 | 32.3 | 33.1 | 33.9 | 34.7 | 35.5 | 36.3 | 0.8 | C | 1.6 | 5.0% | 0.0% | ||
| 75 | 31.1 | 32.0 | 32.8 | C | -0.3 | -0.9% | -0.3 | -0.9% | ||||||
| 80 | 29.5 | 30.4 | 31.3 | 32.2 | 33.2 | 34.1 | 35.0 | 0.9 | C | -0.1 | -0.3% | -0.1 | -0.3% | |
| 90 | 30.0 | 31.1 | 32.1 | 33.1 | 34.2 | 35.2 | 36.3 | 1.1 | C | 0.8 | 2.5% | -0.2 | -0.6% | |
| 100 | 28.8 | 29.9 | 31.1 | 32.2 | 33.4 | 34.5 | 35.7 | 1.2 | C | -0.1 | -0.3% | -0.1 | -0.3% | |
| 120 | 27.7 | 29.0 | 30.4 | 31.8 | 33.2 | 34.8 | 35.9 | 1.4 | C | -0.5 | -1.5% | -0.5 | -1.5% | |
| 130 | 27.0 | 28.5 | 30.0 | 31.5 | 32.9 | 34.4 | 35.9 | 1.5 | C | -0.8 | -2.5% | 0.6 | 1.9% | |
| Avg Diameter from RD 1000 | 32.8 | 0.5 | 1.6% | -0.1 | -0.2% | |||||||||
| Taped Diameter | 32.3 | |||||||||||||
| Diff | -0.5 | |||||||||||||
| Pct off taped | -1.6% | |||||||||||||
| C = scale covers trunk, is continuous | Notes: 1. The 0 column reflects the reading that best covered the trunk as seen by the observer. | |||||||||||||
| G=scale surrounds trunk | 2. Negative clicks shrink the scale, positive clicks expand the scale. | |||||||||||||
| 3. Diameters are in inches, distances are in feet. | ||||||||||||||
| Observations: | ||||||||||||||
| 1. Of 18 readings 3 had potential readings that fall within the advertised accuracy of the instrument | ||||||||||||||
| 2. The average variation of the chosen reading from the taped diameter is 0.5 inches | ||||||||||||||
| 3. The largest variation is 5.6% off from the taped diameter | ||||||||||||||
| 4. Taken over the range of distances and selecting the closest potential reading to the taped diameter yields an average difference of -0.2% | ||||||||||||||
| 5. Talen over the range of distances and selecting the actual reading compared to the taped diameter yields an average difference of 1.6% | ||||||||||||||
| 6. There is a slight difference in diameter readings when using a continuous scale versus a gap scale. ( C vs G) | ||||||||||||||
| Conclusions: | ||||||||||||||
| 1. On average the RD 1000 works well at distances of 45 to 120 feet. | ||||||||||||||
| 2. In close to half the trials, based on how the scale is created, it is impossible to obtain diameter readings closer than 0.3 inches. | ||||||||||||||
| 3.Trials need to been run for a range of diameters before reliable conclusions can be drawn about the overall accuracy of the instrument. | ||||||||||||||