The TDI manual gives examples for dive planning regarding calculating how much gas reserve you should have and what your turn pressure should be (I can email you exert of manual if interested). In their example they do a dive to 30 m on air for 45 m (Vplaner then gives them deco stops with a runtime at 93 mins). The book examples (pasted below) are then based on that hypothetical dive. The problem is that all these examples in the book assume you are not using an additional deco bottle like we are. I provided text below of what is in the manual (rules) and example calculations for their theoretical dive . But what I would like to know is how would I make similar calculations following their rules (see below) when I have a deco bottle? What "rules" should I be following to make sure I bring enough gas and follow a moderately conservative profile? For example, should my gas reserve calculation not be based on getting to the surface but to my gas switch? Should I factor the gas switch into calculating my turn pressure? Thanks so much.

So for calculating their gas reserve they use the following example.

"RULES

1) Begin by planning a dive to the desired depth for the desired time using only bottom gas.

2) Calculate the amount of bottom gas needed.

3) Calculate the amount of transitional and decompression-gas consumed.

4) Multiply the transitional and decompression-gas consumed by two and add it to the bottom gas. The sum represents the total amount of bottom gas that

must be carried for the dive. Note: A diver’s breathing rate should not vary on ascent if he properly monitors and maintains his buoyancy. However, just

as with other phases of the dive, it is possible for a diver’s breathing rate to increase on ascent if he works harder or experiences anxiety.

5) Ensure that the total bottom gas carried is also adequate for allcontingency schedules assuming no gas failures.

If we revisit our sample profile, the dive team needs 3564 L of bottom gas,198 L of transitional gas, and 1477.1 L of decompression-gas.

Total ascent gas needed for one diver = 198 L + 1477.1 L or 1675.1 L

Total ascent gas needed for two divers = 1675.1 L x 2 or 3350 L

Total bottom gas needed including reserves = 3350.2 L + 3564 L or 6914.2 L"

"RULES

1) Calculate the volume of ascent gas needed (decompression-gas + transitional gas) for the diver with the highest SCR to surface utilizing bottom gas for the entire ascent.

2) Multiply this number by two to establish the volume of ascent gas needed for two divers.

3) Convert volume to cylinder pressure

Example:

From the sample profile, the total ascent gas needed for one diver = 1675.1 L.

The total ascent gas for two divers = 1675.1 L x 2 or 3350.2 L.

The team will utilize double 15 L cylinders with a service pressure of 232 bar.

3350.2 L = 112 bar." ]]>