The new Ensign was assigned to subs, where he'd dreamed
of working since a young boy.  He was trying to impress
the Master Chief with his expertise learned in Sub School.

The Master Chief cut him off quickly and said, "Listen, 'sir',
it's real simple.  Add the number of times we dive to the 
number of times we surface.  Divide that number by two.
If the result doesn't come out even, don't open the hatch."