Dostmann HUMIDCheck Mode D'emploi page 13

working on the principle of high frequency measurement.
The instrument is used for non-destructively tracing
dampness in building materials of all kinds as well as for
detecting damp distribution in walls, ceilings and floors.
It is particularly suitable for pre-testing the readiness of
building materials
measurement.
Features
 Quickly indicate the moisture content of
materials

Depth of penetration about 20-40mm.
 Low battery indication
 Auto Power Off
 MAX/MIN Function
 Measure and HOLD Function
 White Backlit LCD Display
Specification
Specifications:
for covering prior to CM