I am looking for a hygrometer that is accurate, reasonably priced, can fit in a quart mason jar, and can be calibrated. I don't care if it's digital or analog. Manufacturer suggestions are appreciated.
There is an option for a round one on the link that measures just 1.75 inches which should then fit through the mouth of a mason jar.
If this for the purpose monitoring and maintaining a good humidity level during cure, you might also wish to consider Boveda 62% humidapacs. They are 2 way disectant packs about the size of a sugar packet that either absorb or release moisture in order to maintain 62% RH. I haven't had even a hint of mold issues since I began using them.