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GPS City Q&A » Outdoor GPS » Foretrex 401 Questions on temperature and altitude?

Outdoor GPS (2 replies)

Item

Original Question

Foretrex 401 Questions on temperature and altitude?

› Garmin Foretrex 401

Author

Reply

Jerry
Winnipeg

Original question asked on Mar 28, 2011, 4:59pm

A few questions:

1) Why does the unit keep incrementing distance when temporarily indoors? For example, stopped at a bank for about 10 minutes, distance kept increasing from 2.10 miles and was up to over 2.6 miles even though I was standing still.

2) Operating temp is down to -20C but even at 0 C, when changing screens, the change isnt' crisp from one screen to the next. ie. The previous screen doesn't completely disappear before the next screen comes up. Is this because the screen is cold?

3) I live on the prairies - pretty flat - but altimeter readings fluctuate from 360 feet to 550 feet and higher. Why would this be?

4) Last question, walking speed fluctuates from 3.0 to well over 6.0 mph and I know I'm not walking anywhere near 6.0 - speed is more like 3.5 mph on avg. Is is possible that the unit is somehow reading arm swing speed?

All in all a great unit but the above quirks are a bit curious. Thanks for listening.

Jordan GPS City
Calgary, AB

Reply #1 on Mar 30, 2011, 7:37am

Jerry,

1) GPS is only accurate for 3 Plus meters depending on the settings and what satellites you are tracking and their geometry. Your position will always fluctuate within an accuracy circle slowly incrementing distance. To eliminate this set your track log to record at an interval larger than the average accuracy. so if your unit is 3 meters accurate set your track log to drop a point every 4 meters or so.

2) The Screen is effected by cold so that would be the cause.

3) The unit uses a barometric altimeter. Barometric pressure changes and that will cause the elevation reading to change. you should calibrate before every use.

4) Not sure on the last question without seeing the problem happen first hand. It could be due to your arm swing but I am unsure.

Cheers
Jordan

Rolan
Bridgewater, NJ

Reply #2 on Apr 11, 2011, 6:51pm

I bought a Foretrex 401 and experience the same altimeter fluctuations one mine also. I had an older Foretrex 201 that was dead on and did not fluctuate like this newer unit.

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