I bought two units, both are useless. If a knob does not work, but that's ok for me because I do not need the clock (!, the product picture is wrong!). The other device has a loose connection. The measured values of both devices are different from Grandma's mercury thermometer and on the implementation of China-cheap goods must be no mention. The required rating can actually be given only for the send Ausklappständer. Works for both devices: - /