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MAP 76 Field Trials-Day 2


Guest Growley

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Guest Growley

Well. I was back on my favorite jogging trail today with the Garmin (you know you're there too much when forestry people ask if you're testing another GPS!). I walked the same trail as yesterday and here are the results. THE GOOD NEWS: I made it a point to ensure that the MAP 76 remained vertical. I walked the course 4 different times and NEVER lost a signal!!!!!!!!!! At one point for about 4 seconds I was down to 2 sats. but never lost a signal..NOW THE QUESTIONS: I marked my car and entry to the trail as waypoints as well as various points along the trail. I could be standing beside a known waypoint (post) and the "map page" would show me 60-80 feet away. When I walked back to the door of my car, after about a minute the "map page" showed me 66.2 feet away while the "sat page" showed accuracy to 13.9 feet??? Am I doing something wrong here? How can the "sat page" show one great reading and the map page (zoomed into 30 feet) show something way off? Still wondering if I should return the unit. I got it Saturday...

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Guest gstrong1

When you marked your position at your car, did you let the unit sit at that point for a couple of minutes before marking it.I found, on a couple of cache hunts, that when I got to the cache location, the III Plus would give me a position reading that was pretty much right on almost instantly while the MAP76 would be off as much as 50 ft.But after opening the cache container & signing the log book(about 5-7 minutes)I looked at the MAP76 and the numbers settled in to what the Plus had given me.Same thing when getting the numbers to post for caches I've placed.Just seems to take a few minutes to catch up.

 

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Gary "Gimpy" Strong

Rochester,NY

 

[This message has been edited by gstrong1 (edited 01 August 2001).]

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You got to watch the marking the car thing. Was the GPS on and running in your car when you drove up to your parking spot? If it was off when you arrived and you hopped out of the car and let the unit lock on and then imediately mark the car. You might have introduce some extra error. When the unit is first turned on it has a lot of book keeping to catch up on. It has to download almanac data for all the satellite and get a good lock worked out so for the first minute or so after the gps locks on I would not expect that the lock would be too good.

 

Another thing to keep in mind with the accuracy rating that the GPS gives you. I'm not 100% positive on this but I think that the number the accuracy data field gives you is a 50% or 65% confindence number. This means that the your actuall position will be with in the radius of that accuaracy number 50% or 65% of the time. If the number Garmin calculates is the 65% confidence number then you need to double it to get a 95% confidence number. So being sixty feet off from the mark you made at your car, although a bit more then you would think, is not unreasonable.

 

Hope this helps

mcb

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