 A third category, mostly used by closed circuit rebreather divers, monitors the partial pressure of oxygen in the breathing mix using a remote oxygen sensor, but requires diver intervention to specify the inert gas constituents and ratio of the mix in use.The computer retains the diver's pressure exposure history, and continuously updates the calculated tissue loads on the surface, so the current tissue loading should always be correct according to the algorithm, though it is possible to provide the computer with misleading input conditions, which can nullify its reliability.This ability to provide real-time tissue loading data allows the computer to indicate the diver's current decompression obligation, and to update it for any permissible profile change, so the diver with a decompression ceiling does not have to decompress at any specific depth provided the ceiling is not violated, though the decompression rate will be affected by the depth.