This hygrometer by Western Humidor is a very small analog hygrometer. The diameter is just 2.25″. The depth is 0.6″.
The case is produced from aluminium and therefor resists corrosion. At the back site is a magnetic mount. A supplied magnet disk can be used to mount it on a wall via a screw. The glass on the front is scratch and fog resistant. But the hygrometer shouldn´t be placed where rain comes directly on it.
The manufacturer reports that the humidity sensor maintains an accuracy of +/- 1 per cent. It is calibrateable by the user himself via a flat head screw. This can be done with a normal screw driver.
The possible usage spans wide. Some use it to monitor the humidity of their guitar collection.