Very high readings like those are often due to static electricity when the jersey is flapping in the wind. Google "flapping jersey syndrome"
. Some riders have wondered if they should call 911!
It's more common in dry conditions, too. Next time you see a reading over 200, try holding the jersey away from the strap for 10 seconds, and see if that helps. Or stop riding, and see if it goes back to normal.
Try wetting the contacts before riding with a drop or two of water, and move the strap a little higher on your chest. Some people have used dryer sheets to limit the static electricity, with varying results.
My Garmin hard strap has been very good, I haven't seen the high readings at all. My old Polar used to do it occasionally.
Last edited by rm -rf; 03-31-14 at 07:02 PM.