FAS-t Cave Survey Device

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Can you shoot pictures of it, with and without the rubber tube in place?

Here you go...

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I ran a few tests on accuracy and error and determined a correction factor for the FAS-t with the inner tube rubber added. the tube adds 2mm to the unit counter so instead of counting centimeters it counts 1.22 centimeters. That works out to about .46 inches per unit count. I measured every two feet for 26 feet 22 inches total distance. And ran some nonstop 26 foot, 22 inches, back and forth, for 19 total tests. the unit varied from 51,52,53 on the counter for each 2-foot segment (52 occurred on 12/19 tests). 706, 707, and 708 were the three readings obtained on the full run test (26 feet, 22 inches).

Let's say you measure a line and get a reading of 1356 units. multiply by 0.46 (or by 1.22 cm if you prefer). 1356x 0.46 = 623.76 inches, or 51.98 feet. What about error? it's plus or minus one unit count, or 0.46 inches (1.22 cm). Basically 52 feet plus or minus a half-inch. Pretty impressive.

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[FW]

OK, post a link to the source

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OK, post a link to the source

here you go....

http://www.divegearexpress.com/tools/arrow.shtml#2870

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[kmev]

Or here: http://nick-toussaint.com/survey__mapping/fas-t

There is an interesting pic of an X1 attached in compass mode. A bubble level attached to provide accuracy for the compass (it needs to be level to be accurate) may work pretty well.

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bubble levels suck. in my hands they do anyway. I can't keep the bubble in the center. I think they are too sensitive with no dampening of the motion. All they do is rock around randomly. Nice for a stationary object, like a table top, but a moving object? By the way, we used the compass of an X1 and found it totally unreliable for surveying. It was relatively accurate, but did not correspond to actual magnetic heading. We contacted liquivision and after some mumbling around they too confessed it was not appropriate for use in survey. This was two years ago, so maybe the newer ones have improved compass.

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[kmev]

By the way, we used the compass of an X1 and found it totally unreliable for surveying. It was relatively accurate, but did not correspond to actual magnetic heading. We contacted liquivision and after some mumbling around they too confessed it was not appropriate for use in survey. This was two years ago, so maybe the newer ones have improved compass.

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Yes, the X1 compass sucks, but I assumed it would be accurate if you were able to hold it level (i.e. the bubble level). Even on a level plane it's not accurate?

I'm differentiating accuracy from reliability in the statistical sense - reliable meaning repeatable (giving the same bearing each time) versus accuracy which gives the correct bearing each time.

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it is reliable. It is not accurate. We surveyed a thousand feet of cave or so and overlayed it on topo map. didn't look right. Jason and ? went back in and redid the survey using Jason's liquid filled compass and card and found the error...if I remember a fairly consistent 20-degrees off magnetic. conversations with liquivision revealed they were aware of the issue and do not recommend it for navigation. But again, this was a couple of years ago, I have no info on using newer versions. But I'd check it against another compass before using it for survey work.

The FAS-t does not affect a compass, at least not enough for me to see any deflection of the needle. So a standard card compass could be mounted on it. I think I'd had an extension of some kind though, it's just the right size for holding in your hand withou much room to mount things on it and still hold it comfortably.


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[MORGAN]

conversations with liquivision revealed they were aware of the issue and do not recommend it for navigation.

A compass that's not recommended for navigation seems like a hammer that's not recommended for driving nails.

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A compass that's not recommended for navigation seems like a hammer that's not recommended for driving nails.

I misspoke. It's not recommended for survey. Navigation is just fine. It is reliable to so you can get there and back, but it's not accurate so your buddies compass may say 120-degrees on the same course that that yours says 100-degrees.

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