with this CF you can tell the computer, that you are planning to stay f.i. one meter below the actual required deco stop depth in order to calculate a more accurate TTS.
I have not turned it off, as the OSTC will calculate a wrong ( to short ) TTS because it presumes you are staying exactly on the required deco stop and not below it when CF16 is off.
I always do my deco stops a little bit below the actual required deco stop in order not to violate the ceiling.
No, it's to make a more precise forecast of the TTS. The OSTC assumes you are going to be at 7m instead of 6m and desaturating a bit slower. You can set this parameter to 0m to disable this feature. But you won't notice a big difference unless you're doing a lot of deco (30mins+)...