Looking at the Buhlmann Model, we see the first compartment to saturate and desaturate is the 5-minute compartment.
Using a rule of thumb derived from this compartment we can predict our first stop depth. That rule of thumb is 75% of the depth for the 5-minute comparment. The 10-minute compartment rule of thumb is 50% of the depth, and the 15-minute compartment is 25% of the depth.
Now that we know our first stop depth is at Max Stop depth, we need to figure out the time we need to spend at that first stop depth to maximize the off-gas efficiency. We know the maximum time should be five minutes, as this is the half-life of the compartment which maximizes the off-gas of that compartment depth. We also know that if we stayed longer than five minutes, we would still be off-gassing, but not nearly as efficiently as the first half-life time, and we may still be on-gassing some of the slower compartments. If we stayed for 25 minutes at the max stop depth, 5 minute compartment X 5 half-lives = 25 minutes, then theoretically that 5-minute compartment would be 97% equalized to the ambient pressure, however it would not be the most efficient use of that 25 minutes, and we would continue to be saturating the slower compartments at that ambient pressure.
But if we stayed for five minutes at max stop depth for that compartment then continued to ascend, lowering the ambient pressure, creating a new gradient and maximizing new 5-minute half-lives for each of the shallower stops, we would create a more efficient off-gassing of that compartment. This would occur at each of the depths shallower than that first stop depth and would maximize efficiency until we reach the 10-minute compartment Max Stop depth at 50% of the bottom depth.
So we create a strategy in which we stop at the max stop depth, stay for five minutes and then ascend, stopping for five minutes and then ascend, stopping for five minutes at each 10'/3m depth above that until we reached the max stop depth of the following compartment -the 10 minute compartment. Theoretically we will have maximized both our 25-minute total deco time frame of off-gas for the 5-minute compartment, and have done the least on-gas of the slower compartments, still without compromising or bubbling. So now we are ready to tackle the 10-minute compartment.
So, how do we determine how much time for each of these stops is needed if you have not reached the max bottom time or max saturation of the slowest of the fast tissue compartments (which is the 30-minute compartment)? Remember, we would need to have a 150 minute bottom time (or more) to reach a 97% saturation, or 5 half-lives of that 30-minute compartment. So we consider a bottom time of 150 minutes or more as full saturation of the five fast tissue compartments. In order to decompress them you would not need to do any more than 5 minute stops from 75% of your depth to decompress the fastest of the fast tissue compartments, and then 10 minutes for each stop for the 10-minute compartment from its max stop depth, and so on. This then becomes MAX DECO Strategy.
But what if we don't do a 150 minute bottom time dive, but something far less? Then we do not need to do five minutes each stop for the 5-minute compartment because it's not fully saturated. So, we could essentially break that five minutes down into individual minutes such as 1 or 2; 3 or 4, or 5 minutes. This time includes the ascent to the next 10'/3m stop. So based on this 150-minute bottom time and 5-minute deco per stops, we could simply divide the bottom time of 150 by the deco time of 5 minutes to get a requisite minute value per stop strategy, per amount of Bottom Time.
So, 150 divided-by 5 = 30 minute Bottom Time for each minute of deep stop. In other words, we have now figured out that for every 30 minutes of bottom time over NDL, you will need to conduct at least one minute of deep stop deco, starting at the 75% of max depth or average depth depending if you are deeper or shallower than the average depth.
Referring to the attached table link below (see page 6 & 7), you can see that if bottom time is up to 30 minutes more than NDL, then do one minute per stop. If BT is between 30 minutes and 60 minutes over NDL, then do two minutes per stop, and if BT is more than 60 and less than 90 minutes, then do three minutes per stop. Remember that this time is for each stop, starting at the 5-minute compartment Max stop depth and then for each 10'/3m above until you reach the 10-minute compartment max stop depth. . .
Now to get stop time for each depth above the 10-minute compartment max stop depth or 50% of your max depth or average depth, you would take the max BT of 150 minutes and divide it by 10 minutes (10 minute half-times), 150/10 = 15 minutes, or each 15 minutes of additional bottom time would require one additional minute of stop time at each of the 10'/3m deco stops above the max stop depth for the 10-minute compartment. Basically you would do one minute per 15-minute bottom time.
Keep in mind that this is for all bottom times even if you are within NDL. So that means to create a proper ascent profile when recreational diving and doing bottom times that keep you within NDL, you simply do one minute stops (including the ascent time) from 50% of your recreational dive depth. So for example, if depth is 80'/24m and your bottom time = 25 minutes, you are within NDL. You would do one minute for each stop depth (10'/3m) starting at 50% of your depth until you reached the surface.
So a proper NDL ascent profile would be to leave 80'/34m and ascend at a rate of 33'/10m per minute until you reach 50% of the depth. Then at 40'/12m, it is one minute. Then ascend to 30'/9m (counting the travel time as part of the 30'/9m stop) and do one minute, then up to 20'/6m and another minute, then up to 10'/3m to do your final minute before surfacing. This is a Proper NDL Ascent Profile and is always conducted regardless of how much time you spent on the bottom as long as it is LESS THAN NDL.
However, if your bottom time was more than NDL, for example 25 minutes over NDL, and you're doing a decompression dive, your stop times would be one minute for each 10'/3m starting at 75% of your bottom depth and then three minutes per 10'/3m stop starting at 50% of your depth.
As a side note, if your bottom time was less than 15 minutes over NDL, then you would do nothing for 75% stop depth and start 1-minute stops at 50% of depth. There is no need for the 75% stop depth and start 1-minute stops at 50% of depth. There is no need for the 75% stops in this case, as the tissue loading is so minimal.
Take a look at the rule of thumb tables (WKPP applied deep stop theory) on p. 6-7 of the attached file link below:
http://www.ultimatedivelog.com/articles/8.pdf