John Bantin has been a full-time professional diving writer and underwater photographer since 1990. He makes around 300 dives each year testing diving equipment.

American cars always include all the features that European manufacturers consider to be extras. When Seaquest came up with the Pro Unlimited, it seems the US company decided to include every feature it could add to a conventional-style BC. There are so many that I apologise now in case I leave any out.
     A fully weight-integrated BC with additional pockets at the rear for up to 4kg of trim weights, it has a large contoured backpack with a moulded carrying handle and swivelling harness-buckles on the padded shoulder straps.
     The waistband and cummerbund are elasticated to compensate for your suit shrinking as you go deeper. The sternum strap is height-adjustable to allow for the position of your drysuit inflator valve.
     Dump valves are operated by pulling on the corrugated hose or, at the right shoulder, a toggle. The lower dump is similarly operated by a toggle threaded through to the lower front of the BC.
     There are two large pockets closed by zips with pull-cords. Six large stainless-steel D-rings are shaped to make them easy to clip onto. A retracting lanyard with instrument clip on the lower left side proved useful for hitching up my pressure gauge.
     A Wenoka Z-lock knife is rigged too, and I mustn't forget Seaquest's self-adjusting lumbar support system, which I am told automatically conforms to the diver's lower back shape. Combined with a neat cushion, this made it easy to stroll about at the back of the boat while waiting to go in.
     I used the Pro Unlimited with an aluminium tank. The trim-weight pockets are so well disguised that I'm sure many owners won't even know they have this facility, and they are a little hard to get to when you want to get the weights out.
     I found it too much trouble to remove the weights at the endof the day, so I left that couple of kilos there, even though it added to the effort of handling the BC between dives.
     The main integrated-weight pockets have been criticised by some for not being secure enough. It's true that they are held in position only by a single slab of Velcro, and in the tropics the flaps tended to get a bit curly after only a few days, so I had to be sure everything was in order before each dive.
     That's not something you would want to leave to a helpful boat crew-member, who might not appreciate the significance of securing the weights.
     That said, if you make full use of the trim-weight pockets and have only, say, 4kg in the ditchable pockets, that might be enough to provide useful lift in an emergency but not so much that the integrated-weight system becomes vulnerable. If you are using a drysuit and need more than 8kg, I suggest you augment the whole system with a weightbelt.
     The side pockets were easy to open and close using toggles, but under water they proved lass capacious than some others and I struggled a little to deploy my reef-hook when I needed it.
     The swivelling buckles meant that the shoulder straps were always at the right angle for comfort, and easily unclipped at the end of the dive.
     However, in common with many BCs with lots of features, the inevitable clutter at the shoulders made getting my arm through the second shoulder strap when donning the rig a manoeuvre usually accompanied by curses.
     The Pro Unlimited sat me high in the water at the surface and, when fully inflated, imparted no uncomfortable torso squeeze.
     However, I prefer a BC that really becomes part of me under water, and cannot say that the overall effect of this one was sleek. It was better than some, and never uncomfortable, but less good than others. The toggles for shoulder and back dumps were always slightly lost through being so close to the other paraphernalia.
     I always used the dump valves and never needed to jettison air by raising the corrugated hose, which always lets water in, so I was surprised to find so much water in the BC after 10 or so dives, making it heavier to carry on land.
     The dive-shop owner with whom I dived also had this BC, and thought it the best he had ever used. It certainly appealed to the owner of the dive centre, the type of man, I suspect, who wants to own the gear with the most features. I still believe that less can be more.
     Available in sizes S, M, L, XL and XXL, the Seaquest Pro Unlimited costs £550.

RELIVE YOUR GAS-SWITCH DIVES ON SCREEN
I am not a computer nerd. Quite the opposite. Back in the pioneering days of the BBC Micro home computer, I used to have to wake up my seven-year-old son in the middle of the night to help me sort out the accounts system I had unwisely installed on it. Today, I am still virtually computer-illiterate.
     So I am the last person likely to want to sit and download dives from my diving computer onto a PC. If you've done the dive, why do you need to go over it all again in arithmetical form?
     Admittedly, the day I found myself doing an unplanned fast ascent from the bottom of Stoney Cove, trying to slow down another diver inverted in his drysuit and with his fins popped-off, I wanted to go over what happened.
     I remember looking at the dotted line on the print-out and marvelling that we had both survived with no apparent ill-effects. However, disasters apart, why bother?
     Then I dived at Bikini Atoll. Most of the wrecks are beyond 50m and to get a decent bottom time of, say, 25 minutes, you need to make a series of very long decompression stops.
     To cut these short, we used nitrox at 80 per cent once we were at 9m and less. This caused havoc with ordinary air computers, and I found I was having to bend a different one on every dive or stay in the water until it got dark.
     The solution came in the form of the DiveRite Nitek3 computer. This is a three-mix nitrox computer, and you can switch manually as and when you change gases. And after 10 dives successfully completed, I began to hanker after a retrospective of the profiles.
     Unfortunately, although the Nitek3 is the most commonly used computer at Bikini, there was no PC interface and software available on the island, so I had to wait until I got home.
     The NitekLogic interface and software seemed extremely easy to install and use. Then I found the first shortcoming of the Nitek3. With a dive sampling rate of every five seconds, it can remember only the details of the past two dives. If I had thought to set it on the maximum sampling rate of once-a-minute, it could have remembered 10, but I had considered that much too coarse a measure for conducting a safe dive.
     So I was left with only two dives, with the last one, 24 hours before flying, atypical. To get full advantage of the Nitek3 and the NitekLogic package, you need to download every day. I'm sure the Bikini Atoll Dive Centre will be getting this facility soon, and had I known better, I could have taken a laptop with me.
     So what do you get as a download? All the usual information and a nicely animated graph of the dive, with gas-switches too, which is quite amusing to watch as it snakes across your computer screen, plotting time against depth.
     However, I won't be taking to religiously downloading dives every day. It's fun, but not that much fun!
The DiveRite NitekLogic costs £109.

If at first you don't succeed
Oceanic brought out a number of new products three or four years ago. There were inevitably some imperfections, but instead of the company soldiering on and leaving it to the consumer to compensate for any shortcomings, it bravely went back to the drawing board and honed its designs.
     Oceanic should not be ashamed. Car manufacturers spend
     millions on research but still have to modify designs after they reach the marketplace. In effect, Oceanic got rid of the sharp edges, and nowhere is this more evident than with its latest Gamma 2 regulator.
     This now has a sleek second stage with no hint of the roughness to the plastic mouldings that we found when we examined the original Gamma 2 in Diver's regulator comparison test of 1998. At that time our panel of testers concluded that the second stage was "over-designed but not over-engineered", and that "the purge button was inclined to stick in".
     That was then. I have no such reservations about the Oceanic Gamma 2 of 2001.
     Sharing the same CDX Enviro environmentally sealed, balanced-diaphragm-style first stage with the Delta 3, the Gamma 2 is the equivalent of its slightly more expensive sibling but without
     the metal trim or the breathing-resistance adjustment knob on the second stage.
     Regular readers will know that I consider such knobs, which are simply spring-tensioners, largely redundant. They enable the user to turn up the cracking pressure needed to open the demand valve initially, but if I want less air I simply inhale less forcefully.
     I must be in a minority, because most top-of-the-line regulators have these knobs. I welcome the fact that the Gamma 2, pitched as a medium-priced product, does not.
     It does have a venturi ± switch, which positions a vane across the airflow in the mouthpiece. This is useful when you first jump into the water and subject the regulator's front diaphragm to the dramatic change in pressure between air and water.
     The vane can prevent the sudden flow of air causing a pressure reduction behind the diaphragm and pulling it in, causing a greater flow of air and ultimately a free-flow.
     Jump in with the venturi lever at the minus position and switch to an uninterrupted flow of air once safely submerged.
     The Gamma 2 second stage is compact, lightweight and beautifully crafted almost entirely of plastic, with a nicely concealed but functional purge control and a mouthpiece that allows the air to flow into your mouth in a broad funnel.
     This mouthpiece is extremely soft and, sadly, did not survive the heavy handling of an aft-deck crew who, I presume, allowed my tank to rest on it at some time and split it. I had to replace it with
     a somewhat less comfortable mouthpiece.
     The Gamma 2 second stage proved extremely pleasant and there was neither too much nor too little air at any time. However, there seems to be no concession to the needs of those who dive in very cold, fresh water, as there is with its Enviro diaphragm first-stage. This is a neat barrel with four medium-pressure and two high-pressure ports and looks ideal for use in the worst conditions.
     Oceanic regulators have always done well in our periodic
     regulator comparison tests. Most recently, the Oceanic Alpha 7 with its piston-type first stage mopped up the competition among regulators that retailed for less than £150. I expected the Gamma 2 CDX Enviro to perform equally well, and I was not
     disappointed. Neither did the tiny exhaust tee irritate me as much as I had expected.
     The Oceanic Gamma 2 CDX Enviro represents a good choice of regulator in its price range and is lightweight, making it ideal for divers who fly a lot.
It costs £215.

CAN A SEMI-DRY LIVE UP TO A WATER PROOF BILLING?
Confronted with the prospect of very long deco stops while diving on the wrecks of Bikini Atoll, I opted to take a warmer suit than I might normally have chosen for water of around 28°C. The tag "Water Proof" seemed over-optimistic but the maker's Aquazor 5mm one-piece semi-dry certainly looked the business.
     Aquazor is some mighty weapon used in cyber-games, which seemed rather inappropriate for what is, after all, protective clothing. That aside, I slid into the suit more easily than an octopus can slip between your fingers, should you be ethically incorrect enough to handle one.
     A rear-entry zip is almost standard now on wetsuits, because there is less chance of water flushing through the back. Here an additional 6mm smoothskin backing flap adds comfort and again resists flushing. And instead of getting that Boston Strangler effect across your throat while waiting in the boat, Water Proof thoughtfully provides a short front comfort zip to relieve the pressure.
     The inside of the neck is also smoothskin, so there is no rubbing. Extra-long wrist and ankle seals in a flexible smoothskin keep the water out, but you don't have to force your hands and feet through them. The outer layer of neoprene neatly zips over them to give a smart finish and can be overlapped by your boot-tops for a flush effect.
     The sleeves fit well because they are contoured and scalloped, with corrugated sections behind the knees and elbows for better flexibility. You don't get that feeling that you have inadvertently included the hanger when you got dressed.
     Heavy-duty rubber knee protection did nothing to counter this effect and those knee pads were handy when accidentally touching down on a rusty deck.
     When choosing a semi-dry, a correct fit is essential. If water can flush through, it won't be semi-dry but 100 per cent wet, and not very warm. This suit was a little large for me, but the seals prevented flushing and I stayed as warm as toast, even during 40 minute deco hangs.
     The flexibility of the modern neoprene used in this and other similar suits means that most people, even me, can now get off-the-peg sizes to fit. Old-fashioned neoprene just did not have enough "give", and we had to settle either for a loose fit that failed to keep us warm, a tight fit with the inevitable struggle, or the trouble of made-to-measure.
     In today's softer material this suit worked not only for me but for my buddy when he tried it - even though he's a lot more portly!
     The Water Proof Aquazor costs £149 with net bag, comes in 15 sizes for women and men, and is imported by the company that handles Tusa in the UK.