The blending calculator takes what is in the cylinder now, the mix you want and the pressure you want it at, and returns the fill as an ordered list of additions in bar. It opens from a gas already in the plan, so the target composition is known before you start.
Current & Target Conditions. Enter the Current Gas in Tank as O₂ % and
He %, with the Current Pressure (bar). Nitrogen shows as N₂ % (auto).
The target composition is read-only; you set only the Target Pressure.
When the inputs are workable the panel reads Ready to calculate blending requirements. Continue.
Blending Instructions. Step through the additions one at a time. Each card shows the action, the amount in bar, and the mix and pressure before and after it.
The sequence
Three additions, always in this order: Add Oxygen, Add Helium, Add Air. Each is a partial-pressure shortfall, how much of that component the finished mix needs less how much the cylinder already holds, with air as the top-up to the final pressure. The helium step is skipped when the target carries no helium.
Amounts are shown as whole bar, the resolution a fill whip and a gauge work at, but the pressure after each step is not rounded, so errors do not accumulate. Any addition of 0.5 bar or less is left out entirely.
What it cannot see
The blend is refused when the current pressure is not lower than the target pressure. There is nothing to add to a cylinder already at or above where you want it.
Partial-pressure blending assumes ideal gas behaviour, and real oxygen and helium deviate from that at fill pressures. It does not model temperature: a cylinder filled fast is hot and reads high until it settles. The third step is air, not nitrox and not a banked mix.
The calculator says so itself: always follow proper gas blending safety procedures and verify final mix with analyzer. Put what your analyser read into the gas, not what you asked the blender for.
Next
- Breathing rates is the next step of the plan.
- Depth limits checks the gas that came out of the cylinder.