Nikon 440 vs LTI Trupulse 200X

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DougBidlack
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Nikon 440 vs LTI Trupulse 200X

Post by DougBidlack » Tue Apr 08, 2014 10:01 pm

I recently measured some small trees that I planted with a 50' telescoping measuring pole and I decided to compare my Nikon 440 with Suunto clinometer and LTI Trupulse 200X to the pole measurements. I made all the measurements at the same time so that I could use orange flagging tape to mark the trees at anywhere from 1 to 5' from the ground. This way my base would be the same for all three methods. I measured most of the trees using the 12.0/12.5 yard clickover point from the base. I figured this would make things easier because I would only have to calibrate the Nikon 440 at 12.0/12.5 yards and also 13.0/13.5 yards (some of the measurements were from this distance from the base). For the Trupulse 200X I used the biggest numbers that I could repeat three times. Sorry about the brevity here, but I'm just trying to get this out quickly after Patrick's great post and I fear I wont post it for a while if I don't just throw this out there. I hope I'm not also lacing this with errors. Attached below are my results from measuring 13 trees using these three methods.
Test.pdf
(19.19 KiB) Downloaded 86 times
Basically, the 200X was mostly within 1" of the pole with a single measurement off by 2" while the 440 was typically within 6" of the pole with a single measurement off by 11". In addition, the 200X tended to shoot dead on or slightly high (1") while the 440 tended to shoot 5-6" low. Percent divergence from the pole was relatively high in comparison to Patrick's work but I believe this was due entirely to the small size of the trees that I measured relative to those that Patrick measured.

Doug

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dbhguru
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Re: Nikon 440 vs LTI Trupulse 200X

Post by dbhguru » Wed Apr 09, 2014 6:58 am

Doug,

Good show. It is comforting to see the results of someone else's test that corroborates my own. The 200X is one heck of an instrument. When LTI quotes an accuracy, they usually give themselves lots of wiggle room. The true accuracy is usually better, often double what they advertise. I'm re-measuring every single important tree with the 200X that I can get to. I'm finding that my existing measurements are within half a foot of the 200X for my TruPulse 360. My 440 is showing its age. It shoots long by about a foot on average.

Any chance you can make it to Durango in August for the conference? I've attached the latest agenda. It is getting better and better.

Bob
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ScheduleSWOldGrowthConferenceApr13.docx
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Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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DougBidlack
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Re: Nikon 440 vs LTI Trupulse 200X

Post by DougBidlack » Wed Apr 09, 2014 9:27 pm

Bob,

yes, it's always nice to have corroboration and I'm so happy that I was able to get within 2" with the 200X as you've often stated that that is what you've been finding. I liked the 200X right away but the more I use it the more I like it. One thing I didn't mention is that I was hand-holding the 440 while I had the 200X mounted on a tripod.

I'd so love to go to Durango and it kills me that I probably won't be able to make it yet again. My mom turns 70 this year and I'm turning 50 so we have some family gatherings that will be taking up all the spare time that I'm not using for tending/planting/measuring trees. It's still not entirely out of the question if I can get a lot done on some weekends but it is probably unlikely.

Doug

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pdbrandt
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Re: Nikon 440 vs LTI Trupulse 200X

Post by pdbrandt » Sun Apr 13, 2014 7:31 pm

Hi Doug,

It is exciting to see the accuracy of the TruPulse 200x. If only it didn't cost $800! I wonder if your Nikon 440 could be better calibrated given that your readings were skewed on the negative side of the pole measured values. One could expect that if the Nikon was well calibrated that about half of the readings would have positive error and half would have negative error. That could account for some of the difference in the error I saw versus what you see. Also, did you average multiple Nikon measurements or just take one?

Thanks for your post!
Patrick

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dbhguru
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Re: Nikon 440 vs LTI Trupulse 200X

Post by dbhguru » Mon Apr 14, 2014 8:19 pm

Patrick

The 200X costs nearly $1,800 instead of $800. But, what a fabulous instrument!

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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DougBidlack
Posts: 425
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Re: Nikon 440 vs LTI Trupulse 200X

Post by DougBidlack » Mon Apr 14, 2014 9:48 pm

Patrick,

Bob has the correct figure for the price of the 200X. It is pricey but worth it for me and I suspect also for Bob. With this instrument I can finally measure annual tree growth from the ground with a fair bit of accuracy. I have been waiting for this instrument for years! I love the 200X but that doesn't mean I don't see room for improvement. Maybe more on that later.

As for the Nikon 440 shooting low, that is to be expected. I think for the clinometer you may be right about positive and negative error being about equal but I think Bob, Ed and others can do a better job of addressing that issue. However, for the 440, it doesn't matter how well you calibrate the instrument as it will still tend to shoot low. This is because you are only making one very accurate measurement. For me this would be the base. I always tend to back up toward a clickover point while shooting to the base. This measurement will be very accurate. However, the top measurement can be off by as much as 17", I think, because it only displays to the nearest 0.5 yard. And it can only be off on the low side.

Here is an example using my 'White Doyenne' pear.
I shot the base at 12.0/12.5 yards which equals 35.00' on my 440. This is likely accurate to within an inch or so.
I shot the top at 13.5 yards or approximately 38.75'
My angle to the bottom was -7.9 degrees and to the top it was +18.6 degrees
So height from the laser to the bottom was 4.81' and to the top 12.36' + 2.00' (height of bottom or base above the ground)
Total height equals 19.17' or 19'2"
Now lets see how much error there would be if the tree were just an inch under 14.0 yards to the top when our laser would still read 13.5 yards. This would mean the top distance was actually 40'2" instead of 30'9" (17" higher). The height from laser to top is now 12.81' instead of 12.36'. This is .45' or 5.4" taller.
The bottom line here is that no matter how well you calibrate the 440 it will always shoot low on average using this method.
You may have noticed that my lowest error was 11" and the highest was 1" so that the midpoint was -5". If I remember right your lowest error was 28" and your highest was 18" so that the midpoint was -5". This seems unlikely to be a coincidence. I'm afraid I haven't thought about this enough or worked enough problems to figure out if this really is just a coincidence. Bob or Ed or Will or Don likely knows the answer.

I only took one 440 measurement from one location.

Doug

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