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, it restricts evaporation from the top surface of the slab; moisture within the slab then distributes itself to achieve equilibrium (due to temperature and chemical interactions from the top to the bottom of the slab).
In the long run, adhesive and flooring are then exposed to the equilibrium moisture condition at the top of the slab. The calcium chloride test does not reflect the long-term moisture situation that will be established by equilibration and can even artificially pull moisture out of the top few centimeters of the slab. Rapid RH® 4.0 EX Smart Sensors predict the relative humidity that will exist after the floor is covered. See the Measuring Relative Humidity at the Correct Depth chart.