Dive computers, decompression dive computers; electronic sensors for monitoring and controlling oxygen, carbon dioxide and/or nitrogen levels and/or gas cylinder pressure in self-contained underwater breathing apparatus; gas cylinder pressure sensors, oxygen pressure sensors, carbon dioxide pressure sensors, temperature sensors, pressure sensors; analytical, simulation and planning software for use with self-contained underwater breathing apparatus, closed circuit re-breathers, and semi-closed circuit re-breathers for analyzing performance of underwater breathing apparatus; Analytical, simulation and planning software for monitoring, recording, control and warning of oxygen partial pressure; Analytical, simulation and planning software for monitoring, recording, control and warning of carbon dioxide content; Analytical, simulation and planning software for monitoring, recording, comparison, analysis and warning of dive depth, dive time, dive profile, ambient temperature, water temperature, atmospheric pressure, time, date, battery voltage, battery status, scrubber status, scrubber duration, scrubber performance, assent warnings, decompression ceilings, decompression times, decompression safety margins and surface interval between dives; Data processors for dive computers and decompression computers; data communications equipment, namely, LED display units and electronic display units for the display of content maintained in digital form, liquid crystal display units, and audible electronic warning devices, namely, mono-tone and multi-frequency piezo operated buzzers and speakers for use with or to control self-contained underwater breathing apparatus, closed circuit re-breathers, and semi-closed circuit re-breathers; computer software for logging, analyzing, controlling and recording information regarding dive statistics, oxygen, carbon dioxide and nitrogen levels, gas cylinder pressure and performance of control self-container underwater breathing apparatus, closed circuit re-breathers, semi-closed circuit re-breathers; computers for use with or to control self-contained underwater breathing apparatus, closed circuit re-breathers, semi-closed circuit re-breathers; electronic or automatic valves for underwater breathing apparatus