Why is the time to surface (TTS) or stop time wrong?
Although stops aren’t always exactly to the minute, this is by design. If you clear to the next ceiling after 10 seconds, it lets you go. It also takes a finite amount of time to calculate the ceiling, so it’s possible for a stop to take a few seconds extra while the algorithm is calculating. The TTS prediction is usually within a minute. With 5 hours of deco, it’s still within a few minutes. First, a bit of an overview of how the computer does this stuff. There are two things going on all the time. First, the compartment loading function uses the actual PPO2 and the actual depth to calculate the changes in compartment gas loading. Second, the TTS function predicts the length of time at the current stop and the total TTS. It does this by using the current PPO2 and the profile. It always assumes that you are going to ascend smoothly at 30 feet per minute to the current ceiling, and then stay at that ceiling until it clears. If you have more than one CC gas programmed, it assumes that yo
