I agree. If you dive, it is logged as a dive. I log not to accumulate dives, but to accumulate information. If it is a short dive but noteworthy, then I log it. I once had trouble equalizing and got to 5 m after about 4 minutes. The dive leader sent me back up. I did not log the dive. Nothing noteworthy to mention. During my rescue course, I was up and down (3 to 5 m) many times but only logged 2 dives over the full day.
Training dives are about learning. Log what you have learned and in my books that counts as a noteworthy dive that should be logged.
Best
GJS
Exactly. The purpose of the log is so that you have your own personal record of your diving. Therefore, you should log any actual dive, and certainly anything significant. I don't think that the length of time matters as much as what happened.
If you put a time limit on what constitutes a dive, then why are two 20 minute dives logged for twice as many dives as one 2 and a half our dive? People who go on to technical or rebreather training may see their dive count progress slow down, as you start doing one long dive while the recreational divers on the same boat are getting two dives in.
Case in point - this weekend, I was having an issue with one of my sensors on my second dive. It was close enough to the other two that I decided to go diving, but to stop at 20 feet and do an oxygen flush to see if it would react to high PO2 (which I can't generate on the surface). Sure enough, at 20 feet, that one was still lagging, and the difference was bigger. I decided to thumb the dive rather than starting with one sensor voted out and relying on the other two, and then I opened the rebreather and confirmed my hypothesis (water on cell #2), dried it out, recalibrated, etc..
So that was a 5 minute dive, but it was a learning experience for me (as a new CCR diver). So that one definitely goes in the log book.