The expression \frac{2 \text{ degrees }}{-3 \text{ hours}}Â, is how it is displayed as a formula, but basically the heat exchange is like a constant? so if its measuring increase in temperature its 2 degrees every -2 hours, and if its decreasing then its -2 degrees every 3 hours going forward in time. I'm not exactly sure what that means but I'm pretty sure its just referring to the BTU output and rising temperature rate in relation to time, or the cool down in relation to the same. Again I am not that intelligent, and could be wrong so don't scream at me please haha.
Hope this helps.
-SpecialK
