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Subject: going overboard on decimals
From: Paul Hirose (71202.2014@XXX.XXX)
Date: Sat Jul 24 1999 - 15:34:22 EDT
I hope everyone realizes that after Silicon Sea runs 3 days without a
fix, including 2 days of severe storm, the tenths of minutes from a
digitally calculated DR are pure noise. Yes, you can copy the digits
off the screen, but they are garbage because the inputs to the problem
are not known with enough accuracy.
Let's assume a day's run is 240 miles, more or less. If average speed
is off by 1%, that's 2.4 miles per day. If course made good is off by
1 degree, that's 4.2 miles per day. Imagine how much worse this gets
when you're being beaten up by a storm.
I reported my results to only 1', and even that was overkill.
Also, there's no reason to worry about seconds of time when dead
reckoning on the high seas. In this case, it's not that you can't
measure time that accurately. The problem is that uncertainties in
the other parts of the DR equation - time and distance - are great
enough to swamp any attempt to figure to the second.
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