ggunn:
OK, but the question was does everyone have to come up when the first person in the group hits 700 psi?
Went down to Cozumel back in late June, dove with Deep Blue, all divers had computers, but varied experience and skill levels. Starting the first day of diving, the DM (Luis) set us up at the briefing, with instructions to notify him by simple hand signals, when each diver reached 2000 psi, 1000 psi-at which time he would float a safety sausage from a reel, providing we were not impared by a overhead obstruction, then to signal him when we reached 500 psi. At that time the diver was instructed to move up the line slowly, make the safety stop and proceed to the surface. 9 out of 10 dives, the boat was within 20 yards of the marker when I surfaced. The other time, it had drifted approx. 50 yards away while picking up a previously surfaced diver. We did this every day during the trip and it worked very well, allowing each diver the freedom to dive their computer. Only if the DM reached 500 psi was the dive aborted and the group required to surface...this happened only once with more than one diver still in the group (there was one girl that I swear had gills, she never came up with less than 1000 psi).
Given the crowded conditions on the surface of some of the more popular dive sites, I found the bright red marker a source of reassurance that other boats/operators could see you in the water.
Our group's over all opinion was the Deep Blue was an excellent operation, they even notified us when someone in the group left any items on the boat, and had them available either at the shop down town, or on the boat the next day for our retrieval.
There are many excellent operators on the island, review some of the other posts in this forum, and make the best choice you can...I'm sure you will have a wonderful time, and yes the warm water will feel like paradise to you!