MacDive Forums

Hi everyone,

I'm having a bit of an issue using the Gas Management tab. I took an intro course on open water sidemount configuration diving (LOVED IT!!!). In this configuration, you have 2 tanks, each with totally independant reg sets (no common fitting like doubles).

I'm trying to enter this in MacDive but I'm not having much success.

Here is my dive info:

• I used 2x aluminum 80s (77 cf each)
  Starting pressure for both is 3000 psi
  On the first tank, I used up 600 psi
  On the second tank, I used up 700 psi
  This was a pool dive and that went on for about 70 minutes
  Average depth was about 10 feet
  I was not wearing my Gekko for this dive so average depth was entered manually in the General tab (maybe this is the cause of the error?)

For side mount, you often switch between tanks (about every 200-300 psi) to keep the tank weights relatively the same (you don't want one rising up and pulling you sideways while the other is pulling you down). Because of how the Gas Management is made, I entered that I switched tanks at half the dive (used one tank for 35 minutes and the other one for the last 35 minutes of the dive).

I'm including screenshots of how I filled in the info for both tanks.

My question is... why is MacDive not giving me "NaN" in the SAC rate column and also why is it screwing up the summary graphic (line goes down and backwards)?
Have I entered something wrong? How should I be filling in the info for my particular case to have it calculate and display properly?

Thanks guys!

Max

How things are implemented now, you would need to create a new tank with the appropriate start/end values every time you switched. IE, the tank you were using at any given time.

I don't think anyone has ever asked why they HAVEN'T gotten NaN. That would be an error! I don't see too much wrong really, your SAC rates seem to be calculated based on the info you have entered.

There isn't enough context to diagnose what is wrong with the summary graph. Send me your MacDive.sqlite data file and I will take a look.

I just saw something else - you say you weren't wearing the gekko. In that case, I assume there is no profile. Therefore the SAC will not be calculated correctly in those cases - you can use the latest beta which will default to the average depth of the dive, if there is no profile. Maybe that solves your problem.

As an aside, what is NaN? Is it a divide-by-zero error or something? I get it whenever there is an unused tank (ie duration of 0).

It means "Not a Number". It's not (necessarily, at least) a divide by zero error.

Various things can cause it. I should put in a check for duration == 0 to just display 0 for the SAC.

Thanks for the explanation Nick. I'll wait for the release of the update (its not urgent).

For the tanks, I think I'll find a way to just sum up everything in one tank as it would be tedious to create a new tank every time I switch (meaning 10-12 tanks for every dive I log... that would get really tedious). So no worries, I'll do some math and figure it out.

Thanks!