I found mine to be NOWHERE near accurate...I recalibrated that thing like every week, and it still was consistently off by varying amounts...Not too sure about the life span of it due to the fact I put it in the closet after a month or so and it is still there. Just my 2 cents...Hope it helps.

On one positive note, it was cool being able to have a power song programed into the ipod, but it was not worth all the other hassle...

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For $29 its great. (I already had the iPod) I don't wear Nike's so I attach the pod to the laces of my Brooks. I am on my second one. Not because the battery died but because I lost the part that goes on my foot somewhere in my house. But after a year it was still working.

As for accuracy I found that out of the box for me it was always showing me more distance than I actually ran (up to 5-10%). I found this to be a good thing because one fun thing that you can do is challenge other people who have the kit - no matter where they are. Because of the challenges I must admit I never calibrated it because of the extra mileage it would give me - my secret is out. However I calibrated it before I ran the St. George marathon. At the end it showed 26.4 miles. I figure that about right on because I turned it on at the gun and I had about .2 miles before I got to the start line.

I don't know the best terrain for calibrating but I did mine on a stretch of fairly flat road and it's pretty accurate. I love mine. I love being able to know at any time how far I've gone/have to go, how fast I am running and at the end, how many calories I burned. I also like the fact that it also plays music, unlike the GPS units. I did have to get mine replaced after I had it for a month, but Apple did it for free.

Rae

I got one at Christmas 2006 and the battery died in August. I calibrated my on a track and it was fairly accurate. I liked how it told you how many miles you had run and when you are getting to the end of your goal, it tells you in increments from of 100 yds starting at 400 yds. It motivated me to keep going even though I mentally wanted to walk the last bit. I am going to try to take the device to Apple to see if I can get a new one. If not I probably won't replace it. I will get a Garmin GPS HRM