An underwater signaling device which has an independent source of pressurized gas can operate regardless of the status of a scuba diver’s air source. Determinations of blood constituent concentrations may be made by comparing absorbance of radiation at varying parameters, such as path length and blood pressure. The head and tail pointers in the host channel adapter include a queue pointer table index and a queue page index for identifying a position within the queue. The first zone can be physically andor optically segregated from the second zone. Thereupon, when the external transmitter 12 is connected to the controller unit 10, it is determined by a determining unit 14 inside the controller unit 10 that the external transmitter 12 is connected to the controller unit 10. The sleeves have a core and cushion grip overmolded on the core.