An adaptor for fitting to a waist band, the adaptor comprising: an adaptor body having first and second ends. A cache implementation uses this ordering to decide what tiles to evict from the cache, i. One buoy 11 displaces water outwards, by the force of its buoyancy, in one container 13, while another buoy 11 displaces water inward, by derivative force acting on it in an outwards direction, in the other container 13. An element can be included in the handpiece to apply a restoring force on the tip so that the tip rests in its optimal position in the absence of external forces. On the other hand, the second backing jig has a circumscribing recessed section corresponding to an inner circumferential surface of the second abutment portion. The outer rim forms a mechanical lock with the rounded ridge to close the upper end of the container during use.