There is almost no correlation between the tests. Relative humidity testing is a measure of the moisture condition in the concrete at 40% (drying on one side) or 20% (drying from both sides) of the depth of the slab per ASTM F2170.
When a floor covering is placed on top of a slab, evaporation from the surface of the slab is restricted; moisture within the slab then tends toward equilibrium (due to temperature and chemical interactions from the top to the bottom of the slab). In the long run, adhesives and floor coverings are then exposed to the equilibrium moisture condition at the top of the slab.
Results of the calcium chloride test do not necessarily reflect this long-term moisture situation. The test can even artificially pull moisture out of the top few centimeters of the slab.
In contrast, using the RH test with any Rapid RH® Smart Sensors will give a reliable measurement of the relative humidity that will exist after the slab is covered. See the Measuring Relative Humidity at the Correct Depth chart.