Product review (2 stars): Not good.
Either mine was missing a part, or this is designed to "click" into a panel that has been punched with the appropriate size hole. It also arrived rattling around in its box; no insert to keep it from doing so, and no instruction slip. It is reading 10 to 12% higher than a hygrometer borrowed from a friend, and another hygrometer I own for a different purpose. This is just not a very good product, although the size is perfect for what I want.