In-situ relative humidity test
A moisture test in which probes are sealed into drilled holes at a specified depth in a slab to measure the humidity the concrete will present to a floor covering.
What does in-situ relative humidity test mean?
Unlike surface tests, it measures conditions inside the slab, which is what determines whether moisture will keep migrating after a floor is glued down. The test needs the building to be at service temperature and humidity to be meaningful. Flooring manufacturers set the passing threshold, and installing over a failing slab typically voids the warranty.
In practice
This is the test that decides whether a schedule slips waiting on a slab to dry, and it is a routine source of conflict near the end of a project.