Anton

Swings mattering more than the absolute number is the part that changes what you buy. A humidifier that cycles is worse than a stable dry room.

Two hygrometers in the same room read eight percent apart, which is worth knowing before you act on a number.

Cheap digital ones drift badly and most cannot be calibrated. If a claim might ever depend on your readings, get one that can be checked against a salt test and record the readings somewhere dated. A log is evidence; a number you remember is not.