measurement in a cold slab

[CC Solutions]

Stephen, where did you get the graphic? It looks like something Bob would have, and it is wrong besides. At least it is wrong in the context you are trying to insinuate.

Without pulling out my psychrometric chart I will go out on a limb and say that graph represents the chart. But concrete RH measurements don't follow the standard chart. I don't know why, and greater minds are working on it.

Service temperature is the temperature the slab will be at during use. Slabs on grade don't vary much, suspended floors can vary quite a bit, especially if the above ceiling space is used as a return air plenum.