Charlie99
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This process is much easier if one uses only the backside of the RDP (the one normally used to find residual nitrogen time; the one with PG columns and rows for Depths). The dive depth + time to PG table 1 on the front side is identical to the Table 3 on the back, except for a couple entries with 1 minute differences because of how rounding was done (or a typo by PADI's).DBailey:The simple answer is that you do a bunch of repetitive dives with a surface interval of 0:00.
Here is your dive plan: Dive #1 = 80' for 10 mins, SI = 0 min, Dive #2 = 60' for 15 mins, SI = 0 min, Dive #3 = 40' for 20 mins.
1. Find your pressure group (PG) for 80' for 10 mins.
2. With this PG and a surface interval (SI) of 0 mins, find your new PG.
3. Calculate your residual nitrogen time (RNT) from the new PG.
4. Add your RNT to your actaul bottom time (ABT) from dive #2 for your total bottom time (TBT) for dive #2.
5. Using your TBT at 60' for dive #2, calculate your PG.
6. With this PG and SI of 0 mins, find your new PG.
7. Calculate your RNT from the new PG.
8. Add your RNT and ABT for dive #3 to get your TBT.
9. Is your TBT for dive #3 less than the NDL for 40'?
For your 3 level dive of 10 min @ 80', 15@ 60', 20 @ 40' the process is as follow:
1. 80' row, 10 minutes is PG C.
2. Move up to the 60' row, staying in Pressure Group C column. The 14 in this cell shows that one reaches PG C after 14 minutes at 60'.
3. Add your planned 15 min at 60 to the 14, getting 29 minutes total equiv 60' bottom time.
4. 29 min in 60' row is PG K
5. Move up to 40', PG K where you will find a 48. That means that, as far as the 60 minute HT compartment, your dive to this point is equivalent to 48 minutes at 40'.
6. Add your planned 20 minutes at 40' to the 48, to get 68 minutes total eqivalent 40' bottom time.
7. That puts you into Pressure Group P.
One can use the pressure group P as your ending pressure group for calculating repetitive dives later that day.
As noted in my post above, one should really be comparing the total bottom times not to the NDL values of the RDP, but to the ML values, which are a few minutes less than the RDP NDLs.