I can also teach deco procedures with no deco gas. Or I can teach it with 27 different gases. It does not say I need to teach any required gases fwiw. I can forgo teaching AN and just teach DP on nitrox 21 should I choose to do so.Right, that's my point. TDI says required to do one deco cylinder but doesn't prohibit two. I'd imagine other agencies do not prohibit going beyond their minimum requirement as well.