I always found the standard 3 litre pony cylinder to be a clumsy addition to my single 12 litre tank, and my buddy with his 15 litre set was even more burdened. I was finding that it was hard to balance the lop sided effect of the additional tank, even by putting counterweights on the other side. So we decided top move to a twin set.

For anybody who has dived using a twin set I am sure they will agree that they are marvelously balanced and feel superbly comfortable in the water. I did and my buddy is equally happy with his, even though we both bought different makes. Me a Halcyon rig and him a Frog wing with Fabers. I on the other hand found that carting 40KG of gear on my back along a quay and into a boat to remove some of the enjoyment from my diving. Furthermore, I was using the twinset for two and often three dives, as I am pretty efficient with my breathing. I also saw that if I was going to do a typical dec dive, say to 40 metres for 20 minutes, I still did not need a full 24 litres of gas if I was taking some higher O2 nitrox down also to decompress with.

I think that it is very important to be comfortable with all aspects of your diving. We find that when we start out, using ill fitting club gear. The difference when we find a BC or a mask that actually fits properly is noticable. The same goes with the size of the cylinders you carry. I started with a 15 litre because that is what everybody had in my club. I found that I was always surfacing with 120 plus bar. So I moved to a 12 litre whjich is fine for most pleasure dives. In fact I use a 10 litre that I blagged from my daughter when she gave up diving – particularly for second dives of the day (I also use it for instructing as it is a doddle moving it around the pool).

So now I have taken to paper and calculator and worked out my likley gas consumption for the sort of dives that I will be doing in the forseeable future. Guess what…twin 7 litre tanks will fit the bill. No, I am unable to get two dives out of them so I will need some provision for the times when I go out on a day boat for two dives (e.g. to the Farne Islands of our North East Coast) but I will be comfortable (and happy) during 90% of my diving.

I considered 300bar cylinders, twin 10 litres, non-manifolded sevens etc etc. Why is there such a choice. In the end I was only able to choose by working out my air needs for the actual diving I was going to do – not what I might or might not be doing in five years time. Now all I need to work out is what computer I will upgrade to!