On Sun, 27 Nov 2016 14:40:54 -0800, Jeff Liebermann
wrote:
I'll take the bet. First, you only need an accurate clock if you want
to obtain your latitude. Longitude can be done with just a noon
sight. Latitude requires a clock.
Sigh. No brain today. That should be Latitude can be done with a
noon sight while longitude requires a clock. Dyslexia induced by
schlepping a 150 lb drill press up about 40 stairs.
I don't want to get into a rant on the accuracy of todays digital
watches. Everything is dependent on the stability of the tuning for
crystal, with is far from temperature stable. I just dug out the
specs for a random Casio wris****ch. About +/-12 sec per month at
room temp and who knows over a reasonable temperature range. I'm sure
someone has done some testing, but I'm late for a free lunch, so you
get to Google for the numbers.
For a common digital clock:
https://en.wikipedia.org/wiki/Quartz_clock#Accuracy
"...a typical quartz clock or wris****ch will gain or
lose 15 seconds per 30 days (within a normal temperature
range of 5 °C/41 °F to 35 °C/95 °F) or less than a half
second clock drift per day when worn near the body."
or a marine chronometer:
https://en.wikipedia.org/wiki/Marine_chronometer#Today
"...even in wrist watches such as the Omega Marine Chronometer,
that are accurate to within 5 or 20 seconds per year."
Incidentally, be careful what you use for a clock. GPS time is
currently 17 seconds ahead of UTC (WWV/WWVB) time:
http://www.leapsecond.com/java/gpsclock.htm
For navigation, you want GMT, UTC or UT1 (all the same). Most GPS
receivers and smartphones correct for this, but not every smartphone
manufacturer got the memo:
http://802.11junk.com/jeffl/crud/GPS-vs-UTC.jpg
Best to check your smartphone:
60 nautical miles = 1 degree of latitude
1 nautical mile = 6076ft
60 NM/sec * 6076ft/NM / 3600 sec/deg= 101 ft/second
Therefore the 17 second difference between GMT and UTC will produce an
error of about 1,717 ft (about 1/4th nautical mile) in longitude at
the equator and lesser errors at higher latitudes.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558