A simple hygrometer (humidity meter) that displays 0 to 100% humidity.
Can be hung on the wall. Diameter 65 mm. Thickness 25 mm. Deviation about + / -7%.
The scale (in German) is divided into four zones:
Grey - zu trocken (too dry = weight loss)
White - Vorkühlraum (Temp +4 to +6 degrees C)
Black - Hauptkühlraum (Temp 0 to +2 degrees C)
Red - zu feucht für Lagerung (too moist for storage)