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post #38 of Old 03-05-2014
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Re: GPS Accuracy - how much is actually needed

Originally Posted by hellosailor View Post
Let's see. With a chart scale of 1:25,000 and a common 0.5mm mechanical pencil, unsharpened, that pencil line would be 25,000 x 0.5mm wide in the real world. 12,500mm at 1000 mm to the meter, 12.5 meters wide.
But if you buy that mechanical pencil at a real supply store it can easily be 0.3mm lead, giving us 25,000 x 0.3mm, which will be 7.5 meters wide in the real world.
I'm not sure if you can sharpen a conventional pencil to a finer point.

Of course if the navigator is using a vintage 5/0 or 6/0 Rapid-O-Graph, they can do twice as well as that.

Personally I prefer the safety zone created by a nice dull Crayola Crayon. (G)

But back to the OP's question: Offhand, anytime you can increase accuracy or precision, that's a good thing. What they are seeing is a signal degradation caused by the hull and deck, and that probably will increase under heavy rain and cloud cover. Ten meters, twenty meters..."Good enough for government work."
I wish you guys were around when I took my ASA 105 test. I was trying to use similar arguments to explain why it was impossible for me to get the "exact" answer that the instructor was requiring of me. He seemed clueless about significant figures, loss of precision due to subtractive analysis, magnification of errors caused by long extrapolation, etc. I still scored 95%, but on the problems where he knocked off points, he seemed to expect me to shoot a golf ball with an arrow from a mile away.

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1998 Catalina 250WK Take Five (at Anchorage Marina, Essington, on the Delaware River)
1994 Mason 44 Firefly on loan from my BFF (West River, Galesville, MD)
1991 15' Trophy (Lake Wallenpaupack)
1985 14' Phantom (Lake Wallenpaupack)
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