A method for signing a dataset in a public key system is provided. A virtual straight line connecting the first and second fastening portions passes through the rotating body when seen in an axial direction of the rotating shaft. The preprocessing may comprise shifting one or more banks before performing an update, so as to create a moving, unoccupied bank or bubble into which the updated version of a bank may be stored. The first case chamber and the second case chamber are fluidly isolated from one another.