In our service package we usually supply you with a hygrometer that you hang up somewhere in the room. Ideal is 50% . But, as long as the percentage varies between 40% (winter) and 60% summer, that's fine. If too much below 40% or above 60%, you can, in consultation with us, consider purchasing a so-called Dampp Chaser, which regulates the relative humidity in your instrument. On request, we will be happy to send you the documentation without any obligation.