Nike Sportband

pocha

If you are using smart phone, you better use the Nike+ GPS (for IPhone) / RunKeeper(for Android).
They are more accurate and free with limited features (but it is good enough for you to measure your run).

I was using the sport band for last 6 months, it has more than 1k+ difference for my every run.
Even I did the adjustment with run and walk, it didn't help.