DIVE LOG AUSTRALASIA FEB 2026

S o, where and when did the first incarnation of the modern dive computer come onto the market? It was probably earlier than you think, and a great deal of trust by divers was placed in those early analog instruments! Read on ... In 1960, Italian engineer Carlo Alinari presented his DeCompression Processor (DCP) at the CMAS General Assembly in Barcelona. It was the first analog dive computer. It was developed in collaboration with engineer Victor Aldo De Sanctis, a pioneer in the field of diving photography and videography, with whom he founded the company SOS-Strumenti Ottici Subacquei (Optical Diving Instruments) in Turin in the late 1950s. At the beginning, they launched the first depth gauges in an oil bath, the only automatic instrument for decompression calculation available at the time. The simple and reliable device was technically based on a pneumatic principle that simulated the saturation and desaturation of tissue in the human body in 120 minutes and indicated no decompression times or eventual decompression stops at depths of 3-6-9-12-15 meters. The DCPs had a plastic or stainless steel case and were manufactured up until 1990, when they were replaced by more advanced digital computers. Nowadays, the early principle may be considered primitive, but for the time it was a real revolution; it became popular with divers all over the world. Inevitably, the material used and some manufacturing defects caused some ‘variability’ in the results displayed, especially on repetitive dives; in some cases, it was referred to as the “Bend-O-Meter”. However, some of the misreadings were not due to malfunctions, but to diver’s bad habits or operation error . To understand the operation of the early instrument, whose case was made of stainless steel in 1964, we must imagine THE ANALOG SOS DECOMPRESSION GAUGES by Des Williams

it on the wrist of a diver during his descent. The ambient pressure inside a flexible bulb within the instrument rises, according to Boyle’s Law, so the excess air inside it is forced through a ceramic filter that simulates the nitrogen uptake and release of a medium human tissue, thus pressurized into a small constant volume chamber. This pressure increase inside the chamber controls a Bourdon tube pressure gauge that, through a mechanism, indicates the depth remaining above which the diver can still safely ascend. In reality, when the diver begins his ascent, the pressure in the constant volume chamber becomes greater than the external pressure; therefore, the gas flow reverses, causing a descending movement of the pointer on the Bourdon tube. The mechanism now indicates the minimum effective depth to which the diver must ascend until the indicator no longer gives the OK to ascend further, or to reach a lower deco stop. This decompression gauge, in its different versions (and thanks to the recognition of this principle) was also marketed by several other well-known diving equipment companies, such as Beuchat , Spirosub , Dacor , CressiSub , Mares , Scubapro , Technisub and others. The Four-Web DCM 4 Decompression Gauge: In 1974, SOS launched the DCM4 with four tissues, based on the DCP principle, simulating the nitrogen uptake and release of four tissues instead of one. Its four elements corresponding to tissues with saturation times from 10 to 40 minutes. Each element had an adjustment knob allowing the diver to enter specific values into the calculation, such as water temperature and dive interval times. During ascent, the diver stops at the first deco stops when the conductive fabric index enters the red zone; when the ‘OK to ascent’ is present the diver can continue his ascent and stop at the next deeper of the four depths as indicated. When all indices leave the red area, the diver may ascend to the surface. The SOS DCK Measurement Device: Released in 1975,

SOS DCS Model Deco Gauge

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DIVE LOG Australasia #416 February 26

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