Most modern diving depth gauges have an electronic mechanism and digital display.

A depth gauge that measures the pressure of air bubbling out of an open ended hose to the diver is called a pneumofathometer.

[1] The French physicist, mathematician and inventor Denis Papin published Recuiel de diverses Pieces touchant quelques novelles Machines in 1695, where he proposed a depth gauge for a submarine.

[3] But it wasn't until 1775 and the development of a depth gauge by the inventor, scientific instrument, and clock maker Isaac Doolittle of New Haven, Connecticut, for David Bushnell's submarine the Turtle, that one was deployed in an underwater craft.

By the early nineteenth century, "the depth gauge was a standard feature on diving bells".

The Boyle-Mariotte depth gauge consists of a transparent tube open at one end.

While diving, water goes into the tube and compresses an air bubble inside proportionally to the depth.

In a membrane depth gauge, the water presses onto a metal canister with a flexible end, which is deflected proportionally to external pressure.

Deflection of the membrane is amplified by a lever and gear mechanism and transferred to an indicator pointer like in an aneroid barometer.

The pneumofathometer gauges are mounted on the diver's breathing gas supply panel, and are activated by a valve.

The "pneumo line", as it is generally called by divers, can be used as an emergency breathing air supply, by tucking the open end into the bottom of the helmet or full face mask and opening up the valve to provide free flow air.

Dive computers have an integrated depth gauge, with digitized output which is used in the calculation of the current decompression status of the diver.

[9][10] The wavelength composition is constant for each depth and is almost independent of time of the day and the weather.

[11] A ratio chromatic depth gauge has been found in larvae of the polychaete Platynereis dumerilii.

[15] Thus, the ciliary photoreceptor cells react on UV-light and make the larvae swimming down gravitactically.

The gravitaxis here is countered by phototaxis, which makes the larvae swimming up to the light coming from the surface.