The new Uwatec computers

When it's immersed in water a Smart computer switches on automatically, and immediately moves into dive mode. When it is switched on manually, all data screens are displayed for 5 seconds. At six seconds the computer will change into ready mode.

Five minutes after a dive is completed the computer goes into sleep mode and does not display any information. The computers are briefly activated every minute to measure atmospheric pressure. When a change in atmospheric pressure is recognized, the display is activated to surface mode for three minutes.

The Smart Com displays tank pressure in the lower display. The tank pressure is also used for the calculation of the remaining bottom time (RBT) and the workload

Air reserve, which should be remaining in the tank after a dive. 30-120 bar or 400-1700 PSI. Default value: 40 bar or 600 PSI

The Smart dive computer allows the diver to manually select one of 6 Microbubble suppression levels. Level zero offers the standard microbubble suppression that is included in the ZH L8 ADT algorithm.

Levels one to level five offer varying additional levels of suppression with level 5 offering maximum suppression. A diver who is diagnosed with a Patent Foramen Ovale (PFO) is recommended to dive on level 5, as are divers who a doing a lot of repetitive diving

Even while asleep, a Smart dive computer is monitoring atmospheric pressure every 60 seconds, only switching on the dive computer when a new altitude sector is reached. There are four altitude sectors ranging from 1,000m (3,000ft) up to 4,000m (13,000 ft)

Usually, we breathe oxygen at about one bar air pressure (which is the ambient pressure at sea level). Air is 21% oxygen and 79% nitrogen so that 21% of the air pressure (0.21bar/3.05psi) is oxygen partial pressure and 79% (0.79bar/11.45psi) is nitrogen partial pressure. At 1,000 metres (3,280 ft), air pressure is reduced to about 0.9bar /13.05psi and therefore, the partial pressures of oxygen and nitrogen are also reduced to about 0.19 bar / 2.75psi pO2 and 0.71bar/10.30psi pN2. The body has to "outgass" the excess 0.08bar/1.15psi of nitrogen. As a matter of a fact, moving to a higher altitude is a decompression to a lower pressure and it takes the body about 18 to 19 hours to desaturate the surplus nitrogen. The time needed to adapt to the new partial pressure of nitrogen is called adaptation time.

The engineers designing Smart dive computers considered this adaptation time as an integral part of the algorithm for altitude diving. Therefore, even while they're asleep a Smart is monitoring for changes in atmospheric pressure.

Air pressure is measured every minute and classified in four different sections. These sections are displayed on the screen as small mountains. Depending on previous dives and the actual ambient air pressure, the decompression model calculates the adaptation time (or desaturation time to equalize the nitrogen pressure in the body to the nitrogen partial pressure in the ambient air).

The adaptation times depend on the "saturation history" of the diver and the speed of altitude changes. If we assume that there was no previous dive, the adaptation time is about:

18 to 19 hours for altitude section 1 (ambient pressure above 905mbar / 13.12 psi)

26 to 27 hours for altitude section 2 (ambient pressure above 815mbar / 11.81 psi)

32 to 34 hours for altitude section 3 (ambient pressure above 725mbar / 10.51 psi)

If the diver returns to a higher air pressure (lower altitude), we have a reversed situation. This situation is similar to a shallow dive, because the body has to saturate with the excess nitrogen in the air. Of course, the body has also to adapt to this new situation, but the Smart will not display an adaptation time because the adaptation time of the Smart dive computers has the meaning of a desaturation time. A desaturation time is only displayed, if at least one of the tissues is outgassing.

Even while asleep, a Smart dive computer is monitoring atmospheric pressure every 60 seconds, only switching on the dive computer when a new altitude sector is reached. There are four altitude sectors ranging from 1,000m (3,000ft) up to 4,000m (13,000 ft)

1st Figure: Mountain with 4 bars, 850 m / 2790 ft

2nd Figure: Mountain with 3 bars in the top, 1650 m / 5413ft

3rd Figure: Mountain with 2 bars in the top, 2650 m / 8694ft

4th Figure: Mountain with 1 bars in the top, 4000 m /13120 ft

To minimise Microbubble formation, the Smart shows at the surface the altitude ceiling that the diver is prohibited from exceeding, following a dive. Useful for divers who dive in mountainous regions, this is displayed as a flashing altitude segment which corresponds to the altitudes displayed above, and is subject to the preset Microbubble suppression setting in the Smart.

The dive planner allows the diver to plan a dive for any Nitrox mixture up to and including 100% O2. It considers the maximum depth (including the Maximum Operating Depth) for a given mixture, the best mix for a given depth for a given mixture, the maximum dive time and the CNS 02% at a given depth. It also considers the residual nitrogen levels from a previous dive.

Starting from a depth of .5 meter (1ft) current depth is continuously monitored and updated in .1 meter increments; depth and dive time, maximum depth and the no stops time. Also the temperature affected tissue saturation is calculated and the no stops time and the decompression requirements are determined.

The ambient temperature is constantly displayed and monitored as an input into the ZH - L8 ADT MB algorithm

Starting from a depth of .5 meter (1ft) current depth is continuously monitored and updated in .1 meter increments; depth and dive time, maximum depth and the no stops time. Also the temperature affected tissue saturation is calculated and the no stops time and the decompression requirements are determined.

The maximum depth is only displayed if it exceeds the current depth by more than one metre (3 ft). This prevents frequent changes of the maximum depth when diving in the vicinity of the maximum depth.

The ZH-L8 ADT MB decompression model considers eight body tissues as well as the diver's conduct and the ambient conditions. This allows for an even more accurate prediction of the likelihood of decompression sickness. One specific example of conduct considered by the computer where a diver misses a decompression stop and spends less than three minutes on the surface. A missed decompression stop can cause the formation of microbubbles and massively increases the risk of decompression sickness. In this particular instance, starting at 13.6m (45ft) the diver has been instructed to complete a decompression stop at 3m (10 ft) for 3 minutes. However, because the diver has temporarily ascended to .9 metre (3ft) and failed to complete a decompression stop, the computer has now advised two decompression stops. The first is at 6m (20ft) for 5 minutes and then on completion of this stop the diver is advised to stop at 3m (10ft) for 9 minutes.

The need for a deco stop is indicated when the No Stop time reaches zero and the zero starts flashing. The No Stop indication is now replaced by the "Deco Stop" indicator with the dive computer displaying the decompression stop depth 3m(10ft) and the duration of the stop, which is expressed in minutes. If there are multiple stops required (for example 6m(20ft) and then 3m(10ft) then the computer will indicate the deepest stop required. On completion of the final decompression stop, the no stops time goes to 99 minutes.

The need for a deco stop is indicated when the No Stop time reaches zero and the zero starts flashing. The No Stop indication is now replaced by the "Deco Stop" indicator with the dive computer displaying the decompression stop depth 3m(10ft) and the duration of the stop, which is expressed in minutes. If there are multiple stops required (for example 6m(20ft) and then 3m(10ft) then the computer will indicate the deepest stop required. On completion of the final decompression stop, the no stops time goes to 99 minutes.

Smart is always calculating decompression stops and when a Microbubble suppression level has been selected, it is also calculating the necessary level stops. Should a level stop and a decompression stop coincide, then Smart displays two symbols "Deco" and "Level Stop"

Aladin dive computers are programmed to allow an ascent rate of between 7 m/min and 20 m/min, (23ft/min and 67ft/min) dependent on the depth.

The Smart Com calculates the diver's workload and considers the oxygen fraction of the inhalation gas mix. If a diver has reached a pO2 of 1.5 bar, without workload, the O2 toxicity increases by approximately 1% per minute. In this case if there is a very high workload this value increases 10 fold to 10% per minute. For example if there is no workload the diver could stay for 100 minutes, but with a high workload the time is reduced to 10 minutes. It is therefore important that when the lung symbol appears that the diver relaxes the breathing rate.

If the depth of a recommended level stop is exceeded by more than 1.5 m (5 ft) then the Smart cascades down to a lower Microbubble level. The Smart now displays the new level until the end of the dive as well as any new level stops that would normally be expected in the lower level.

If the Microbubble level has been reduced during the dive, the indicated Microbubble level will continue flashing for five minutes after reaching the surface.