Bob DBF
Contributor
It's easy to forget. My first post-certification dive was about 2.5 months after my last certification dive, and I initially set the tank up backward (valve on the left). I knew it didn't quite seem right and it worked ok, but couldn't figure out what was wrong until someobdy else pointed it out (rather pointedly, too!). 12 more dives in 5 days reinforced it to the point where I probably won't do that again. It doesn't help that I'm left-handed, and having the valve on the left seems more natural to me.
And actually, now that you are certified, you can set up your rig any way you want. For your own tanks you could just get a left hand valve for doubles and cap it, end of problem.
Bob