For those of you who wonder at the many alternative rangefinder brands floating around on amazon and ebay- Uineye is one you may want to cross off the list, at least for tree measurement. I've just packaged mine up to return. Specifically, I purchased this unit: http://www.amazon.com/Golf-Rangefinder- ... 6T1GN3ACEW
I was initially very enthusiastic about this rangefinder- measuring solid targets it is very consistent and seems at least as trustworthy as my Bushnell. A whole slew of other attractive features aside, the best thing about it was its ability to consistently read very fine twigs in the crown of trees that my Bushnell simply would not, and to do so through very small gaps (in fact, if any other unit I ever use is as good at this Uineye at hitting base trunk of a tree through tiny gaps in dense brush, I will be ecstatic). Those same fine twigs, unfortunately, are its downfall.
For whatever reason- when reading an individual bare twig, especially at ranges of 40-70 yards, the Uineye returns a spread of differing figures that I believe can probably be carefully interpreted to get a near-correct height most of the time, but the more I use it the less comfortable I am with having to entertain that uncertainty every time I measure a tree. I had intended to do a controlled test to pin down its behavior but after an impromptu testing session I'll detail further I simply don't think it's worth it. For the same price you can (and I will, ASAP) get one of the newer Bushnell units that seem much more capable than mine.
Today I was in the neighborhood of the Clove Lakes Colossus tuliptree, whose crown is highly visible from all directions and who I've spent enough time with to believe that even with the Bushnell's reluctance to read bare twigs, my previous measurement of 126.6' tall (especially considering that the Bushnell rounds up) can probably be regarded as a maximum possible height to get out of that tree.
Selecting the highest leader, I pulsed the laser a few dozen times and informally recorded the trends in the numbers I was getting back. The majority of the readings fell between 58 and 60.5 yards, and within that range certain numbers repeated more often than others. The most conservative of those was 58.2, which I selected as the number I would keep in accordance with my use of this unit to this point. Outside of that range were the high and low outliers- it might be one thing if the outlier readings were just occasional, but the high and low outlier ranges probably accounted for a quarter of the figures each. High readings went from 62 yards up to 63.2, and low readings went from 56.5 yards down to 55.3.
Crunching the numbers, the reading I selected from the "normal" range yields a height of 125.1- not bad, in comparison to the Bushnell. Other readings in the normal range would put it within a couple feet. This reinforces my confidence that the measurements I've made with the Uineye so far are probably pretty accurate, but I will be checking them all when possible nonetheless. If one were to just use the highest number they'd get a height of 134.3, nearly 10 feet over, or to assume the worst and take the lowest reading you'd get 119.5. That disparity of nearly 15 vertical feet in the readings returned by the Uineye from a single twig (no wind) in the course of a few dozen pulses just strikes me as unacceptable, even if careful interpretation does *probably* yield accurate figures.
Measuring conifer foliage this behavior is much less pronounced, with just occasional and clear outliers rather than the mushy range of readings it returns from bare twigs. Solid targets like tree trunks, buildings etc. return highly consistent readings, so it's not as if the unit is worthless across the board- just not sufficient to the needs of accurate tree measurement.
On my way to the Colossus I used a trail I previously had not and it went through a section of slope with rich-seeming soils and trees that were obviously very tall even before I got out the Uineye- the trees there are some of the tallest I've measured on Staten Island. A beech to 119.4, American Elm to 111.8, pignut and bitternut hickories each just a hair under 122' and red and black oaks from 115' to more than 120', and yet more 130'+ range tulips. All of this is tinged with regret that I can't fully put my faith in those numbers, as careful as I was to discard outliers. For all I know, the twig structures of some trees might be more prone to producing outlying numbers than others, which could confound my technique of selecting a conservative figure from the "normal" range. At the least, all of the trees I've measured with the Uineye are on Staten Island and all could be revisited in the course of a single afternoon. Any resulting discrepancies will certainly be noted.