Hi All, My Girlfriend and I are currently nose deep in learning to dive and have managed to get stuck on using the RDP card to calculate minimum surface intervals. In particular there is one example we can't understand; it's question 7 on the chapter 5 knoledge review in the open water diver manual. The example results in a pre second dive PG of M and a post dive PG of P. These two letters don't match up in table 3. Should you assume that this means the min surface interval between dives is zero? Surley that can't be right? Can anyone help? Thanks, Ric n Ros.