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76csx And Electronic Compass Accuracy Or Lack Of?


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Anyone else with a 76csx or 60csx had a chance to try and check the accuracy of the electronic compass?


I played with mine a little yesterday and the average seemed to be about 20 degrees off using sight and go, after multiple calibrations in two different areas. I used a bruton 8099 and a brunton geo transit to check it against which were consistantly within 1 degreee of each other and multiple readings taken. It seems consistantly off, in that repeated measurements are consistant.


I'm going to test it out a little today in a couple new areas but if that's all the better it can do that's pretty unimpressive. The other thing I noticed is that the unit seems really sensitive to tilt, I had a 76s and it's compass seemed pretty good but I never did check it as far as using the sight and go feature. I also don't remember it being this touchy to tilt, we are talking a +- 10 degree difference if the unit is tilted 1/4" from level which could be easy to do in the field, especiallly without a "hold level" warning. The 76s also had a warning screen if you did not have the unit level and I don't see this on the 76csx either.


I will test it out some more today and see what I get.

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I did some more testing today, and I think the main issue is the units over sensitivity to tilt. If I calibrate it on a flat table by turning it in circles instead of myself turning holding it, then leave it on the table and sight an object say out the window, it's within a couple degrees of my other compasses that have sighting functions, certainly acceptable. The north also points as my other compasses do if you have the unit on the table, but it's hard to resolve small angle differences that way.


The problem is that if you change the tilt of the unit lets say 1/4" total (the front going up 1/8 and the back down 1/8 or vice versa), which is easy to do when you are trying to sight something with it handheld, you can easily get +- 15 degrees from from what it should be. Most likely minus since that's the error for having the front tilted too high, and is the tilt you would have to sight something that is above ground or to see the sight marks. In fact if you really want to make it angry try going about 3/4" inch and my unit would easily vary 100 degrees.


I realize that electronic compasses like to be held level but this seems extreme to me.


Just for an example, I sighted an object that was ~255 deg (254 on one unit and 255 on another, probably a declination adjustement dispute)


For giggles I took 10 readings spaced over the first part of today to try and get a feel for my repeatability of my measurements, trying very carefully to make sure I have the unit level. Doing so I could keep the error to about +- 7 degrees but that's still pretty bad if you ask me. If you tried to do a rough trianglulation on a map using two measurements that were both off 7 degrees the result would be pretty ugly even for a rough ballpark.


I realize it's not a transit compass but I don't belive my 76s was that touchy with the compass and small amounts of tilt, or it may just be that the level warning on the 76s kept the error down.

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You would think Garmin would learn from Magellan and use a tri axis compass. It drove me nuts to try and get the level indicator to say I was holding it level. I figured out that in a Vista when it's sitting flat it's not really level. Using the compass to point at the cache was not as accurate as just using the pointer while moving.


It looks like the same issues carried forward.

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Yep, it would certainly seem for a feature they charge an extra $50 for it does not perform very well in actual use. It may well be that with further practice and getting an idea of a couple tricks or references to make sure it's level accuracy can be increased a lot, but it should not be that hard. It's capable of being very accurate and repeatable if it's held perfectly level, but that's not an easy task.


I can tilt my brunton 8099 that 3/4" of an inch and get errors in the 2-4 degree range, and that's so much tilt it's hard to sight with it. My brunton geo transit is even less touchy 1-2 degrees tops with enough tilt it's almost too much to even use it as recommended. Of course it also costs nearly what the 76csx does. I suppose garmin figures it gets you in the ballpark, and it's not designed to take highly accurate sighting measurements. If they built in a little more resistance to tilt error though it would be a killer feature.

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