An auto-focus compensation method, adapted to an image capturing device having a touch screen, includes the following steps. The bottom sensing device includes a pipetting probe spring mounted to a pipetting arm of the pipetting station. By selecting a BS with a certain level of unused ranging slots, the MS may exponentially decrease the ranging overhead when compared to a conventional MS that does not consider a BS’s ranging overload when trying to perform ranging with the BS. In response, the first computer decrypts each encrypted segment using the associated key.