Yes Linus, gas pressure can indeed go up during a dive

At first glance it seems logical to make the ending pressure be the
lowest pressure observed during a dive. But if you do valve shut down
drills with a tech setup (where you have a fully redundant double
tank setup with two valves, two regulators and a manifold in between),
then you continue to breath from what is indeed the same "tank", but still
the valve on which your air pressure transmitter sits does get shut down
and de-pressurized. So your pressure goes down by quite a bit, and then
comes back up when the valve is turned back on.

And the ending pressure of the dive (which is used for things like the SAC
calculation) is indeed potentially higher than the lowest pressure
observed during a dive.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>