Surface displays

We asked our testers to observe the computer's surface displays for ease of understanding. We asked them if the computer scrolled no-stop limits too quickly (it scrolls from 15 to 60m in 3m increments in around 50 seconds) or if the log or planning functions were hard to understand. Only four of the testers scored this feature, giving it 85%.

Other features

The Aladin Sport user can recall the last 19 dives using the computer's own log or, for a more detailed permanent dive record, use a PC interface to download up to 37 dives. This provides a graphic profile of the dives, tissue loadings and personal details such as your name.

In addition to the usual pre-diving scrolling of the Sport's no decompression limits, there is also a built-in basic dive planner. This can only be used when the Aladin is saturated to predict no-stop times for the next repetitive dive. You cannot simulate a dive by selecting a depth and stopping there, as on more expensive computers; but you can see the effect user-selected surface intervals will have on your repetitive No D limits. It is more helpful and informative than the real-time scrolling on other budget machines. This can be used to plan air supplies or 'What if ...?' scenarios.

The Sport also indicates both time to fly and total desaturation time. Score for other features was 80%.

Bench Tests

We are intrigued by the 'smart' algorithm that is the heart of the Aladin Sport. It is claimed that this algorithm can recognise potentially dangerous profiles and either take measures to reduce bubble formation by decreasing no-stop limits, or requiring earlier or longer stops, or actually warning the user to stop diving altogether until the computer 'thinks' the diver's physiology has returned to a safe level.

Because of the risk of deliberately making provocative profiles to observe how the Sport would react, we rejected manned testing. Instead we ran the sport through its paces in a pressure chamber alongside an Aladin Pro, which uses the previous non-adaptive ZH - L62.1 algorithm as a control.

In all, we made five dives. These took place over two days with a maximum survace interval of 18 hours so that neither computer desaturated. These included multi-level, no-decompression dives that we ran to within a minute or two of the no-decompression limit at each level to simulate wall diving, yo-yo profiles that simulate an instructor carrying out free ascent training, shallow dives followed by deeper dives and saw-tooth profiles. On most dives we exceeded the ascent rate warnings.

There appears to be little difference between the no-stop times predicted by the older Aladins and the new models. Throughout our sequence of dives the non-decompression levels predicted by each computer at the beginning and end of each surface interval were within a couple of minutes of each other at all depths below 15m. At shallower depths the variation could be up to 8 minutes less time on the Pro.

Under pressure, the computers occasionally varied. On different dives, either the Pro or Sport could provide more conservative remaining no-decompression limits. At one point the Pro required a oneminute stop at 3m while the sport showed 12 minutes remaining no-stop time. On another dive the Sport required decompressing when the Pro did not. We suspect this was a result of the smart algorithm feeling that we were pushing our luck. Though the computers made the same potential dives, the Pro logged a 6 minute shorter surface interval than the Sport after dive 2, for reasons we do not understand. It also read half a metre deeper. We do not think this affected our tests measurably.

The logs from the Aladin Sport indicate that some of our profiles were suspected of causing micro bubbles in sufficient quantity for the machine to consider them influential. It would be interesting to put the Sport through a multi-day series of dives, which we suspect would show increasing conservatism.

However, what was very striking was the difference between the old and new algorithms when we checked their predicted No Fly and Total Desaturation Times. Dive I (multi-level for a maximum depth of 40m for a total dive time of 48 minutes) resulted in a No Fly time of 4 hours for the Pro and 11 hours for the Sport. Desaturation times were 13.52 minutes and 24 hours 17 minutes respectively. Throughout our tests the Sport called for far longer No Fly and desaturation intervals than the Pro.

The chamber profiles we ran fly in the face of accepted decompression wisdom. The Sport appears to take some measures to help protect a diver from his own foolhardiness by requiring stops and extending desaturation time, compared to previous Aladins. However, we cannot underscore strongly enough the fact that tables and computers do not get bent or have consciences. It is up to the individual diver to make his dives as safe as possible. We recommend all divers read up on the subject of decompression or take a computer class to thoroughly acquaint themselves with accepted safe diving practices.

The Aladin Sport is a very highly specified entry-level computer. It offers many features normally associated with far more expensive machines. We suspect that we are witnessing another major advance in computer design. Time will tell.

Manufacturer's reply:

'Readers can be assured that we were very sure of the benefits of the adaptive decompression model before we embarked on a development programme lasting five years and costing US $10m! Statistics had then revealed no significantly higher risk when diving with computers than dive tables, despite computers in general suggesting longer dive times than tables. Also, roughly half of decompression incidents were occurring within dive table limits.

'The numerous influences on the decompression of the diver make our decompression model complex. The calculations have to be done on line and are therefore beyond the practical scope of dive tables. The ZH-L8 ADT is the first calculation model able to respond to risk situations. It is used in all the current Uwatec computers, which are identifiable from earlier models by their download-to-PC facility.' John Sinclair, Managing Director, Uwatec UK