Was there life before computer?

calculating instruments before the digital era

Underwater slide rules

The scuba diving pioneers had only a simple decompression nomograms, invented by the US Navy during World War II, but since 1988 there are slide rules that allow to maximize the diving.

Only recently, after years of experiments with complex analog devices, is appeared some small computer that can perform underwater calculations, but the dive slide rule, dubbed The Wheel, is always taught in the training courses.

Diving decompression table

These tools, a mixture of classic slide rules and nomograms, are needed to plan the maximum period for diving according to the depth achieved and calculate the decompression times needed to dispose the excess nitrogen accumulated breathing compressed air.

A wrong decompression can cause severe sickness, often fatal: on ascent the pressure drop cause the nitrogen dissolved in the blood to expand and form bubbles, and the diver risk a dangerous embolism. Must therefore emerge slowly, with calculated stops based on the length and depth of the dive, according also with the gaseous mixture breathed: air, EANx (oxygen enriched air) or Trimix (oxygen, helium and nitrogen).


The Wheel, scuba slide rule ready to use and in action

One side of the slide rule is intended to calculate the time that elapses between two dives, or between a dive and a plane trip. The decompression leaves in fact for several hours a small amount of nitrogen in the blood, normally of no consequence, but which should be considered in case of repetitive dives to avoid accumulations. Also inside an aircraft the pressure is lower than at sea level of ca. 25% and all the nitrogen must be disposed before the flight to avoid an embolism. These calculations are to be carried with precision and it would be better to use The Wheel only on ground. Underwater the oxygen become toxic, procuring loss of attention: a wrong situation for work with a slide rule, but now dive computers are very cheap and widespread.


Scuba-diving analog calculator, 1970 and modern digital model

Nicola Marras 2008


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