Using the Testo 0636 2135 Thin Humidity Probe, protective PTFE caps, and a compatible Testo measuring instrument, it is possible to carry out an equilibrium moisture measurement. Ideally, moisture equilibrium is measured in a bore hole in a material. To keep the bore hole as small as possible, the 0636 2135 Humidity Probe has a diameter of only 0.16 in. The probe should be protected from dirt by a Teflon cap during measurement. The bore hole is then simply sealed using sealing clay.