forerunner 305 ascent/descent calculations?

[Hazy]

As indicated in title I have a foreunner 305 by Garmin that I am beginning to use for training/data keeping purposes.

In riding the same route on 3 different occasions it has come up with 3 completely different ( not even close ) results in my total ascent/total descent columns. Am I wrong in believing total ascent is the total in ft. of elevation climbed during my ride and descent is total in ft descended during the ride? The route begins and ends in the same spot and does not cover the same areas twice.

Can someone explain to me why on this route the ascent/descent numbers are not the same on the same ride and why they would differ so much between rides?

Sorry for my thickheadedness if this is a simple minded question. /img/vbsmilies/smilies/duck.gif

Hazy

 

[Hazy]

Hmm. Well, am I at least correct on how ascent and descent is calculated?

 

[Phil85207]

I am sorry I can't help you but there is a Garmin forum that may have someone who can. By the way I had a 305 for years and loved it. I did not have your trouble, but my numbers of assent and descent did not match those ridders who had more expensive units. One other thing is if you mount the 305 on the bar you must take care it does not leave the bike if you hit a pot hole. That is a common problem with the bar mount and I lost mine that way once and it met a cruel death by the tire of an SUV. My wonderful wife got me a 800 as a replacement as I had a birthday coming up. Good luck.

 

[poky]

As i understand it the GPS system is not that good at determining elevations. I get the same sort of results with my 305. If you use the excellent application Sporttracks to track your rides, their is a plugin application to correct elevations. My understanding is that it works by comparing your route with topographical models. The version 2 of Sporttracks was free, but they are charging for version 3. I'm not sure if version 2 is still available for download. There are numerous other plugins as well.