A reference chamber for a fluid sensor comprises a housing, a deflectable structure, which is arranged movably within the housing, a control device configured to drive the deflectable structure at a first point in time such that the deflectable structure assumes a defined position, and to drive the deflectable structure at a second point in time such that the deflectable structure moves out of the defined position and a movement of the deflectable structure in the housing is obtained. The reference chamber comprises an evaluation device configured to determine a movement characteristic of the movement of the deflectable structure on the basis of the moving into the defined position or on the basis of the moving out of the defined position and to determine an atmospheric property in the housing on the basis of the movement characteristic.