Hot air does cool according to the laws of thermodynamics, but sure ok the laws of the universe are suspended in this thermal chamber because of this mystical housing, that must be what it is protecting the part from, and it is a reflection that the OP fails to mention, why would it give a consistent reading of 85? SO this reflection is also amazingly consistent? The entire part on all sides has the same reflection? Wouldn't it or shouldn't it vary significantly based on anything that would impact the reflection? You are assuming that not only that this reflection exists, but that all of the variables that influence this reflection remain constant and unchanging because the result is unchanging. How improbable is that? You are welcome to make as many assumptions as you like but there is not reason that I must make the same assumptions or agree that your assumptions are correct.