Equilibration occurs when the air in a drilled test hole stabilizes with the rest of the slab. The thermal and moisture levels equalize with the slab, if the slab's relative humidity (RH) changes the test hole will change with it. For the accuracy of the readings it is necessary to wait until equilibrium is restored after drilling.
In most cases the Rapid RH® 4.0 EX Smart Sensor will be within 3% of the final reading one hour after installation. However, the ASTM F2170 standard states that the test hole must be covered for 72 hours before an official RH reading can be documented.
Please visit http://www.wagnermeters.com/flooring-moisture-meters/concrete-moisture/ for more information or call 1.800.634.9961 to talk to a professional.