The Temperature difference, part result is the difference between the top and bottom temperatures.
It is top minus bottom; therefore, a negative number indicates the bottom temperature is hotter than the top temperature. This result is also only available for Midplane models as there is no bottom temperature result for Dual Domain.
The difference between the top and bottom temperatures of the part should be within 5°C. The larger the temperature difference, the more likely the cooling will contribute to the part warping. This is known as differential cooling.