Calibrating Foot Pod w/Garmin FR220 -- automatic? (Read 27 times)

I'm finding that the internal accelerometer doesn't seem to be all that accurate, at least for me.  I think I don't move my arms in quite the same way when on the dreadmill as I do outdoors -- just tried my first treadmill run with the 220 after months of strictly running outdoors, so it should be good and calibrated.  In reading around it seems like this is not an entirely uncommon thing with runners.  So the FR220 is reading what feels like a solid minute/mile slow.  Can't even go by the dreadmill, since that is WAY WAY off (but it was free.  It only reads in MPH and that seems to be about 2mph off.  Previous owner's experience concurs).  One reason I purchased the 220 a few months back was for that accelerometer.  Meh.

Anyhow, I do have a foot pod languishing in a drawer.  I know with older Garmin units the calibration required running on a known distance outdoors (ie on a track or a rural 1mi. stretch of road) with GPS disabled.  But it appears that one calibrates the FR220 with GPS enabled.  Has this worked well, or would I be better off manually calibrating (as I ask I'm not even sure that's an option)?