A long-term experiment on the load bearing structure of two identical replica of a clavichord from 1807 is carried out. One clavichord is stored in a showcase with nearly constant exhibition room climate. The other one is stored in a climate chamber and loaded by a weekly changing climate of about 30% and 80% relative humidity. By photogrammetric methods, the instruments’ displacements are measured every week over a period of two years. Within a numerical study, the first humidity cycles are simulated by the finite element method applying multi-FICKian hygro-mechanical material models with respect to short-term response and without viscous phenomena for the first instance.