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GPS to check speedometer


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Was on a friend's boat this weekend, and he was showing off a GPS he just bought. A hand-sized Magellan 12-satellite model he bought for $99. Besides the postional info, it was giving speed data. Constantly updating the speed in tenths of mph.<P>Hmmm - wouldn't this also be a good way to check speedometer accruracy in cars with modified drivetrains? Just run the speedo to 60 or whatever and glance at the GPS speed. Then you know if the speedometer is accurate or not. Seems to be a better way than running over measured distances....<P><P>------------------<BR>

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Guest John Chapman

It's a perfect way. You can calibrate any speed, too. 60-80 would probably be best, though because I don't think our old speedos are going to have linear error rates.<P>Also a good excuse to buy another gadget. GPS handhelds can be had for as low as about $50 now.<P>Additional uses: <BR>Manifold vacuum correction for altitude (-1 inch/1000 feet above MSL)<BR>Compass correction (we all have one of those, right?)<BR>Get one with a moving map display and never get lost. There's even one now that has a voice chip in it and will give turn by turn directions to a selected destination. Don't think that one's under a 100 bucks, though.<P>Cheers,<BR>John<BR><P>------------------<BR>John Chapman<BR>BCA 35894<BR>1965 Skylark Convertible (Some Assembly Required)<BR> jmchapman@aol.com

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What stores are you guys hitting to get GPS for under a hundred bucks? I've never seem them for less then $200. :/<P>Oh the wonderful uses for new gadgets. smile.gif<P>Many Thanks!<P>Scott.<BR>

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Guest John Chapman

Scott...<P>1. Typo in my post $150 instead of $50<P>2. Start with this link:<BR> <A HREF="http://wireless.cnet.com/cgi/crunch/pcompare2.asp?tag=st.cn.sr1.ssr.cn_gps&ptable=GPS" TARGET=_blank>http://wireless.cnet.com/cgi/crunch/pcompare2.asp?tag=st.cn.sr1.ssr.cn_gps&ptable=GPS</A> <P>There are a number of products under $200.<P>Cheers,<BR>John

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I hadn't thought about using GPS for speedometer checks, but it might work pretty well. Consider that the whole GPS thing was a US military situation to locate our troops without using radio transmissions and supposedly have an accuracy of 25ft. I understand the civilian version's tolerance is a little greater (50-100 feet maybe).<P>The less expensive handheld GPS units are typically sold in hunting stores or stores that sell hunting equipment/items. Some do have the "where I've been map".<P>The GPS units which have driving instructions are somewhat more expensive and typically have dedicated vehicle installations. These instructions will have detailed distances between turns, etc. The same driving instructions and distance information can be found on many of the map sites on the web which have driving instructions as part of the site.<P>Another way to check for speed and distance is the G-Analyst item that uses accelerometer information and an internal clock to compute time and speed items. It is typically used in autocrossing to measure lateral G forces in cornering and other driving activities. It's price is still under about $200.00 and would have more vehicular uses if you don't go out in the wilds hunting or camping.<P>Enjoy!

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