While I am a believer in computers, when people say that tables are only good for non-realistic linear profiles then I am a bit lost. When was the last time, you guys did your typical SAW-TOOTH bounce dive in which you went to 105 feet stayed for 10 minutes then went up to 20 feet for 15 minutes followed by 70 feet dip for 11 minutes and back up again for 30 feet for 21 minutes? Who dives that way? Yes there is a variation in depth when we swim across an uneven terrain but …
Lets be realistic. Keep in mind that SDI version of US Navy tables give you 60 minutes of bottom time for 60 feet depth. This means that as long as you are not diving deeper than 60 feet and not staying more than 60 minutes in the water, you are within the safety bracket that your 500 dollar UWatec computer will "calculate" and tell you. You can go up and down and still not need a computer or even a table as long as you remember two numbers in your life and those are 60:60. Stay above 60 feet and stay within 60 minutes and you are good without any computer or table.
What about the next dive of the day? Do I need a computer? In reality my typical surface intervals are never less than 60 minutes and rarely more than 1 hour and 44 minutes. So a typical, relaxed surface interval which goes over an hour does not change anything in the 60:60 rule for the next dive. If you wish to split hairs then a surface interval of an hour applied to the above dive only removes 2 minutes from the max bottom time at a depth of 60 feet so after an hour of surface interval you are doing 58:60 instead of 60:60. Big deal! In all practicality 60 minute dive to a depth no more than 60 feet followed by a surface interval of 60 feet is repeatable cycle that requires no computer or table.
I honestly do not see any point in having a computer for Open Water diving which is confined to 60 feet anyway. The only reason why Open Water divers believe that “tables only calculate square profiles and computers are essential” is because their instructor at the dive shop is also a sales person for UWatec or Alladin Pro etc. He gets commission when he sells OW students a dive computer. This is why we have divers who are so knowledgeable in high tech solutions while not knowledgeable in the problems those high tech solutions are really solving for them.
60 matters some places but not so much in others. Most of the dive sites I dive off NC the bottom is 80-100 ft. I see lots of OW divers on the 80ft dives and some on the 100 ft dives such as our ledges. A popular dive with NEW OW divers is the Hyde. Bottom at 80-85. Top deck at 60. A typical dive may spend some time at 60, some time at 80-85, some time back up at 60. I have instabuddied with new OW divers on the Hyde and they had maybe 4-6 quarry dives prior to our meeting up. And now a there are usually two dives a trip and the SI is about an hour. Second sometimes on the Markham where you are varying from 40 on top to 85 in the sand but everybody hits the sand to see the big props.