I'm seeing that discrepancy between the elevation data from Garmin Edge 305 and my Ciclosport when I only run the Garmin data thru Training Center.

Through MotionBased, bah, forget about it! (unless you want to impress yourself with how much you really don't climb ) I didn't know there was a way to correct it though - I'll look for that adjust button.

The data on my Ciclosport tends to agree moderately well with Bikely mapping, and if anything might be a bit on the low side (maybe 10% lower than elevation gains from Polar). So as long as it still works, I'll take elevation gain off my Ciclosport.