Not quite as "good" as the professional league like the GANN Hydromette BL Compact B. However, you do not know exactly how these work with these devices. I have the equipment needed to measure the residual moisture in anhydrite before the floor was laid. Unfortunately, no match was to evaluate this case correctly. However, can be used here also the table of GANN devices (in my case, the GANN Hydromette BL Compact B). Show almost the same values. The TFA was a little more optimistic here.