this is an article from last year but once somebody told me "teaching is reapeting", hein Christophe :-).
Next to that I would like to mention a new rule for surface intervals introduced by Richard Wonka, AIDA Instructor Trainer and very active AIDA education commission member. This is his formula:
|Dive Time X maximum pressure (in bar) = surface interval|
So I would encourage you (and especially the spearfishers among us) to follow Richard's formula. As he told me, the results of this calculation matches the hold formula (depth -in meter-/5) but it is also more conservative for longer dive.
Have a nice day!