Posted by Wayne on July 23, 2001 at 21:11:28:
In Reply to: Computer vs tables for bottom time posted by Steve on July 22, 2001 at 17:52:48:
You have a problem with the PADI RDP. Since you hit 91 fsw you must round up to 100 fsw which has an NDL of 20 minutes. You blew the NDL by "no more than 5 minutes" so you must do an 8 minute safety stop at 15 fsw and stay out of the water for 6 hours.
This is the problem of tabular calculators like dive tables. They assume square profiles because you might do them. This makes them too conservative for normal recreational profiles. This is why the computer gives a longer bottom time -- because it averages. When we violate the instructions of the tool (table in this case) by making up our own mental average we are assuming that we are doing a good job and will outsmart the tool. It can be risky and the cost of error can be great.
I prefer the machine measuring and averaging the depth for me! I'll take the computer. The one thing that I wish they do was allow you to isolate the faster "tissues" and see the reduction in nitrogen on ascent. That would be a better way to see if the stops were in the right ballpark. But alas that might be a bit complicated for most and the instructions for computers are already too long for anyone to actually read.
Wayne