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Browsing through the NOAA diving Manual (1991) section on repetitive diving,
 one find the following paragraph;

"NOTE

	There is one exception to the Residual Nitrogen Timetable for
Repetitive Air Dives: when the repetitive dive is to the same or
deeper depth than the previous dive, the residual nitrogen time may be
longer than the actual bottom time of the previous dive.  In this
event, add the actual bottom time of the previous dive to the actual
bottom time of the repetitive dive to obtain the equivalent single
dive time."

	If I understand this, and I may not, it says that for
repetitive dives, where the residual nitrogen level is longer than the
second dive itself, the actual bottom time should be the sum of the
two dive times at the second depth.  While I can understand physically
why this exception might be the case, I wonder if the complications
that this rule induces might be the reason why PADI and others teach
the "second dive shallower" rule to avoid confusing students.  Second 
dive shallower allows divers to follow one algorithm in using the 
tables.

	The second inference from the NOAA note would be that second 
dives deeper have greatly reduced bottom times if there is significant
residual nitrogen time from the first dive.

	Of course (?), the computed algorithms probably take this into 
account...

	Does the full DCIEM manual have a similar exception?


		Peter David

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