Polar FT 40 way off on cals burned

LongIsland27itl

Hey guys, I just got my polar ft40 in today, I worked out for an hour, lifted weights for 30min and did cardio for 30 min (stairs) and the hrm said I burned 850 cals which is just too high and can't be right. I did my vo2max test earlier before the gym and my own index came in at 57.

I entered my data such as age height weight correctly, what could be the problem?
There's no way I burned 850 cals in an hour of mild weights and cardio, I'm in good shape.