After reading through materials on diving and just recently diving with some folks from Europe (not counting the numerous work related experiences I’ve had with people in Europe), it is my impression that the two existing systems, Metric and Imperial creates an as sharp division in the diving community as it does in all other aspects of life. My own dive education has almost exclusively been in Imperial to date. During a recent dive with some European divers, I had to admit to myself, that communication with the dive teams was complicated by two factors:
1) at that time my gauges were exclusively reading PSI
2) I’m not as fluent with the Metric system as with the Imperial system
Metric System
For all of you that do not know the history of the Metric system, let me cover it here. The Metric system was developed in France. Leaving aside the nationalistic motivation to counter the British dominance in world politics, the main criticism that was raised was that the Imperial system lacks a simple conversion between various units, especially among macro and micro measurement systems. The Metric system was developed as a simplified solution that linked macro and micro measurements in a very concise and easy manner (e.g. going from kilometers to nanometers is a meter of decimals, while the same step in Imperial would involve numerous odd conversions). Kind of reminds me of the arguments between DIR and the mainstream diving industry. 
Onto Imperial
At this point in time it is my firm belief that the Imperial system is on a slow but steady decline world wide. In diving, the two system create a division that complicates an effective knowledge transfer. When traveling outside of the US, most average divers will have a hard time getting accustomed to Metric units. Why does it have to be this way? I supposed that you all agree, based on the various publications on pressure/tank sizes/gas volume, that the Metric system is by a huge account easier to apply when trying to make quick calculations at depth or during dive planning. Just because the USA and UK is still used to apply Imperial units because it became customary, should this prevent the diving community from recognizing that the simplicity of the Metric system is preferable, especially when your health might depend on quick thinking and decisions under water? As with DIR, the Metric system is fighting a tough battle in most Imperial countries, even though the majority of people in these countries recognize the benefits that the Metric system offers.
As a group that seeks excellence in diving skills and the ability to calculate independently of tables and computers, would it not make sense for us to have a stronger emphasize on Metric calculations? At the very least, I would see much benefit in planning dives in BOTH systems, as to give all divers in our group the ability to freely move with confidence between Imperial and Metric dive sites. One step further would be to push for a general change in the dive industry to increase the effectiveness of communication worldwide. If a small group can prove the value of switching to Metric, this can consequently be spread in the whole dive community over a period of time. Again, the main thought is to make things as simple as possible to understand and to promote independence of electronic devices or tables. From a technical standpoint this switch would be very easy for us; as most of the technical dive equipment you possess has the ability to read in both systems.
Dive Safe,
Duane Johnson
Precision Diving
About Duane Johnson
I’m a Brit living in the US, and I have encountered this problem in reverse. All my training and my gauges etc are in metric and now i have to constantly deal with the conversions. But I stick doggedly with metric nonetheless, because it’s just harder to screw up – especially if you or your buddy has had a situation which throws your pre-dive planning out of the window and you’ve got to do recalculations at depth.
I’m from Germany (all metric) but I live in Okinawa, Japan (metric as well) but I bought many of my gear from Americans living here so the gauges are all in imperial, of course metric is far more easy but imperial is fine as well once you remember the conversation like 14.7PSI = 1 bar, etc.
I think it’s good to know about both systems (gauges) because if your buddy suddenly shows you his gauge in a system you have no clue about, how would you know when it’s time to go back or dive shallower etc.
I’ve never understood why, exactly, dive training is in metric in the U.S. to begin with. Ok, the average person has no intuitive feel for “20 meters” but then our intuitive feel for “60 feet” is misleading. 60 feet is the distance across my yard. I don’t worry about if I can make it across my yard, but 60 feet under water is a whole new level of danger.
And then there are the tank units. No one has a good feel for what a cubic foot or a p.s.i. is, so these are just as easy to learn in metric the first time around as imperial.
I can’t do either set of gas calculations in my head (well, not easily) so I figure I’ll just stick with metric and it will come to me as I need it.