Abstract: An apparatus for carrying by a diver while under water (and at the surface between dives) provides information useful for enabling the diver to ascend therefrom both expeditiously and safely in order to avoid decompression sickness. A corrosion-resistant ceramic transducer (60) provides an electrical capacitance responsive to the pressure of the water thereon, in an electronic circuit (52), comprising also a resistance (61), for providing a signal (at 53) responsive to the time constant therein and substantially unaffected by normally encountered variations in supply voltage. Electronic data processing means (40-51), responsive to the signal, computes the water pressure, the depth of the transducer (60) in the water, the minimum depth to which the diver can from there ascend safely, the minimum time within which the diver then can ascend safely to the surface of the water, and the elapsed time since the beginning of the dive. Displays (48, 49) provide indications to the diver of the computed values.