Product review (4 stars): Very helpful
When I realized I wanted to keep better control over relative humidity, I looked into getting measuring devices. It turned out there are "top end" ones, some of which are actually scientific instruments and some of which may not be worth the price. Anyway I was pleased to buy several of these for a fraction of the price at the local ubiquitous W merchandiser. I had several locations that needed them.

True, they don't always agree with each other, but they are close enough. And I did do comparison tests for a while. Now I just let these little guys tell me when I need to lug the dehumidifier around, when there's about to be a fungus amungus.

Let's see, I've had these for at least eight years and so far no battery replacement. (Hope that statement's not a jinx.) They have a cute little holder. But I just stand mine on a surface that is convenient for viewing.