I’ll start with what I consider my biggest mistake ever. I’m not proud of it and I hope none of my instructors read it but here goes: I planned just a fun dive with a friend I don’t see often. I loaded my gear and headed to the site. I had been diving a lot in the weeks before so the gear was set and tanks were filled with the same mix each time. My friend and I had a nice time talking and catching up and I was a little distracted. We put our gear on and did the dive and had a nice day. When I got home and unloaded I noticed in shock that the mix label was 3% more than I thought was in the tanks. In my haste and disctraction I forgot that I had changed the mix on my last fill from the one I had been using and had nicely exceeded the MOD of my mix. Fortunately I dive 1.4 and we didn’t stay at depth long so all was well. I realized I could have easily died that day though. It was a lesson well learned. I bought a nitrox analyzer and have made it a rule to analyze my gas just before I attach my regs EVERY time I dive. The lesson here is never assume and complacency will get you hurt.