In Reply to: Disagreement with Ken's article in CDN posted by MHK on April 26, 2007 at 07:56:08:

I haven't read the article in question, but I'm assuming it is referencing a swim-through from one entrance of a cavern/cave and exiting the other side. 1/3's calculation start at the beginning of your dive, soon as you go under, not at the entrance of the cave or cavern.

Regarding the statement:

"Once you hit that one-third mark, if you haven’t made it halfway through, turn around. If you’re past the halfway mark, you can continue through to the end."

How does a diver know that they have reached the halfway point? If you have never made this dive before, can you assume that the remaining of the passage will require the same gas as the 1st "half"??. The answer is NO. What if there is a restriction or something else that may cause a diver to use additional gas than the first part of the dive. To safely enter a cave through one entrance and then exit via an alternative entrance you must enter one way, follow rules of 1/3s, and leave a marker once you've reached your 1/3s turning point. On a 2nd dive, you must enter via the 2nd entrance and you must reach the marker that you left on the previous dive at, or before, your 3rds turning pressure. If you don't follow this procedure, you are just assuming you are able to make it through the passage based on personal judgement and that can lead to serious problems. After you've done this once YOU KNOW YOU CAN MAKE IT. Training will teach you save caving, not an article.