Formula for % of Fat Burned vs. Polar Monitor's Number

endlessendless

I just upgraded from the Polar RS100 to the RS200 because I wanted the ability to have more than one exercise file's worth of data each day. Unfortunately, the RS200 does NOT provide me with the % of Fat Burned along with my calorie expenditure the way that the RS100 does. Does anyone know of a formula I can use to determine % of Fat Burned? There must be a way if I have all of this other heart rate data.