As I said CP6 directed me to this page : Currency Heat Map - Forex Trading, Currency Forecast, FX Trading Signal, Forex Training Course, Education, Tutorial, FX Book, Forex ebook, Learn to Trade Forex, FX Guide, Pivot Points, Currency Rates, Forex Secret, Forex Brokers, Currency Trading Sys

Their definition of "heat" is (I changed the colors in the default settings and a way symbol pairs are constructed - this way you can see relative strengths in both directions) :

strong up : current close is above prior bar high
weak up : current close is above prior close but less than or equal to prior bar high
no move : current close is equal to prior bar close
weak down : current close is less than prior bar close but greater than or equal prior bar low
strong down : current close is less than previous bar low

regards
mladen