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None of the discrepancies below are going to cause a make or break situation. I'm just looking for a little education for future reference and safety.

I measured an object today at 384 (+/- 17) feet. The height on Wikipedia (I know I shouldn't trust the internet) is 361 feet. This is only a 6 foot discrepancy if you low ball the error. Still, I was thinking I would get something a little better than more than the maximum error. If you take the reading at face value it is a 23 foot difference. This may not seem like a whole lot, but if you have that error at a 150 foot object it could end in some serious injuries.

Is the discrepancy most likely to be operator error, a problem in the measuring device, or an error on Wikipedia? Is this much error typical and considered acceptable? It is a little unnerving to me. Can water cause a larger reading than normal to come back?

How did you shoot the object? Straight down from the exit to the point of impact?

Is it possible that Wikipedia is measuring the highest possible height (i.e. from appurtenances or with lowest water level, or something)?

361 feet? Get off the computer, stop being a pussy, and jump that shit!

I took two measurements from the road of the bridge. One straight down into the water and again over land. The other measurement was to the top using the Pythagorean theorem. I then added these two together.


Using the measurement over land, rather than water, there was a difference in about 10 feet, and the structure is grounded on two concrete pads, which would definitely account for the rest of the discrepancy. I am thinking this clears it up.


I'm actually planning to jump from a lower exit point on the object. Doing a rollover or TARD into water so I'm much less concerned about the precise height. Still, I want to remedy the problem for the future.

My friends and I use Nikkon lasers, and out of the two one is ten years old and one is near new. Both give the exact same reading 99% of the time. Maybe it's your laser. Maybe it's your technique. If you are super concerned about it get a second opinion from another laser.

there are certain lasers on the market that will compensate you give you horizontal reading, i had to get a new one because i was shooting objects fromthe base and it was giving me the horizontal distance even though i was shooting vertical. Got a Nikon one know and its great.

I got the cheapest range finder I could find and I don't think it has any added features like that.

Do you think you just answered your own question there?

Most range finders are very accurate, even the cheap ones. If you plan on using this as a potentially live saving device, get a good one. I have purchased two over the years and have found them to be very accurate. I use my suunto as a reference as well and find them to be within a very small margin of error. If your range finder is made by any recognizeable company, and you were standing on top and shooting straight down, I would trust that over any measurement listed anywhere.

I certainly considered the quality as a possibility. The manufacturer (Wildgame Innovations) lists +/- 1 yard as the error. I'm just trying to identify other potential factors. I will test it against another Bushnell range finder that I have access to.

I was also just thinking about yard vs meters, as the range finder I have can do both. Yards are a smaller measurement, allowing them to provide a finer resolution than meters. Yet another argument for Tom to use against the metric system and why America rules the world (joking of course).

I have definitely noticed a discrepancy in readings, depending on different surfaces. I don't have too much experience shooting over water though.

I found this little nugget a while back when doing some research, it might help: http://www.millettsights.com/...ser_Rangefinders.pdf

any one tell me what a good price model rangefinder is that displays height of objects coz with my luck ill end up with one that doesnt

Wow, this is EXTREMELY helpful. Thanks for the article.

Any time you introduce math into it, you are just adding measurements of additional angles or distances, and the small inherent errors in each of the data points is going to get multiplied to a bigger error in your end result. Keep the height measurement as direct as possible, to avoid that.

Yes, you're right, it did enhance the inherent error in the measurements, but based on the calculations I did, there is much more error than I should have had.

If anyone is interested in the way error increases with the Pythagorean theorem (or any equation), check this out:

http://en.wikipedia.org/...ainty#Simplification

In my case, where I measured 229 to the top and 219 to the bottom, I had an error of +/- 16, even when the device only had an error of +/- 1. That's how much combining two measurements effects it.

What do you define as a small margin of error? I have also used my Suunto as reference and noticed as much as 30-40ft difference on a 300ft object. I use is for a "ball park" double check, recognizing that the discrepancy as a % will be higher for lower objects. Are your discrepancies much smaller than my example?

Gorillaparks, the Suunto is only acurate if you can climb faster than the air pressure changes.

https://www.youtube.com/watch?v=9ie8VEtQHmE

Pretty much...

I think we both know how long it can take me to climb a 300ft ladder...

Well not specifically directed at you, but partly as a general PSA-- a lot of that advertised "+/- 1 yard" stuff can be nothing but crap. Like any other measuring instrument, if you really want to interpret the information it gives you, you need to compare it yourself, against known benchmarks and relevant environmental conditions.

The supposed advertised accuracy of +/- one yard... what the heck is that supposed to be? a 95% confidence interval? a 99.9999998027% confidence interval?* does the manufacturer even say? probably not... the marketing people are not engineers. It may have nothing to do with accuracy or precision at all, but just tell you where the digital display rounds out the number to.

The question in this case is not, "is my device inaccurate?" but "exactly how [in]accurate is it?" But if you are smart enough to accurately quantify your total error, you already know this

Now, for sure, I think most people find these things pretty accurate in general practice. And most jumpers just trust the number and have never had any problems. But if you doubt its trustworthiness, then absolutely like you are doing, start asking questions. But that is just the first step. The hard work is actually going out and testing the machine and seeing how the scatter plots compare to benchmarks.

Just curious, did you compare the pythagorean calculations with a tangent calculation using an inclinometer measurement? There are some rangefinders that do angled measurements automatically, if I ever get one it would probably be one of those.

*not just a random number, btw

Edit: I just re-read this post, no I am not actually that anal-retentive / OCD

this one is pretty accurate, but it's a little on the cheap side. i don't like cheap shit.

http://www.amazon.com/...K0PYyRLLlRoCyn_w_wcB

for that price ill buy a few of them

The technical density of the words you are using is hilarious. I did not use an inclinometer, as I do not have one on my range finder or otherwise. I definitely like what you said about the question being "how inaccurate" rather than "is it inaccurate". I plan to test that out, but I'm wondering what the best pre-measured distance I can find is.

How long till this devolves into "define IS"

http://en.wikipedia.org/wiki/Barometer_question

http://www.esmerel.com/...estion/building.html

Haha I realized that, what can i say, I like data :)

Do you have a nearby sleepy community airport, preferably without a control tower? Just walk in to the airfield office, the field manager would probably be willing to take you out on the runway where some accurate distance landmarks should be available. If it's not too busy- usually it's not.

Devolve means ' to gradually go from an advanced state to a less advanced state'. When you define each and every word so there is no ambiguity then you are at the highest level of understanding instead of being in a low level of guesses, inaccuracies and misunderstandings. Clinton was showing us how to handle grand juries and that everyone can understand and see things differently at different times. Define 'running' for me. It could mean so many things... is the car running, are you running, is the politician running, are you running a business, etc.

Yep, Contracts and Torts can be verbal jiu-jistu . . .

but in this instance, estimating object height,
measuring an object to inches or centimeters
does NOT increase safety margin since we ALL
jump with systems that have variances that
well exceed those minor measuring errors.

As in, I can look up a 7 digits FCC number,
laser the object, zero my Suunto, AND keep
accurate count of the number of rungs I climb
which in aggregate will tell me how high I am,
but a Go & Throw can take from 50 to 100 feet
based on air density, canopy weight, temperature,
field elevation, etc. You buy gold, it is accurately
weighed, you buy pot in Jamaica and the guy just
puts a hand full in an old scrap of paper . . .

I can't the be the only guy who thinks it is nuts
to sweat a bit of differences for any jump that is
over 100 meters or 328 feet, on the flip side, the
difference between 140 and 160 feet is noticeable,
especially if you are big and jump 12 pound wings.

Oh well, to each their own, I just had a 3 IPA lunch
with my awesome wife, my buddy Gordon (C4 quad)
celebrating 56th birthday, and Paul (paraplegic) who
has 4000 jumps, 20 BASE jumps, 2 post injury, so
the beer and heating pad me chuckle at this thread

It depends on how close the altitude is to your personal threshold. If my hand held vs stowed line is 300ft, then +/- 30ft becomes more relevant then on a 500ft bridge, etc.

The obvious choice is to pick the conservative altitude (270ft) and plan accordingly...

I agree that there are other variables that can impact a jump just as much as object height, but I'm not really too concerned about the exact height for this object. What I AM concerned about is understanding how to effectively use the tools I have available. In this case, the 30 feet difference doesn't matter to me, rather I care that I may not be properly using a system that will factor into my decision making in the future. Every jumper reaches a level of proficiency that they are comfortable with in a particular area and then learn to trust that skill. I haven't reached that point yet with measuring object height.

Football fields work great

You guys are silly, I test my laser with my opening height every jump. I'd quit jumping if I wasn't so worried about keeping my laser accurate.