The Corneometer® measures in arbitrary units from 0 (no water at all) - 120 (on water). The units have been very well establishes as so called "Corneometer units".
The penetration depth of the electric scatter field is demonstrably very small, so that only the moisture on the skin surface is measured. Measurements before and after covering a measuring area with a special foil (15 µm thickness) show that on the foil only 20 % of the original value are measured, the total measurement depth is approx. 40µm. The superficial measurement is important because especially the moisture content in the Stratum corneum is interesting for cosmetic applications.