what does the menu item Gas On/Off in the Deco Setup do?
Hi Agility,
Originally in the Predator, the only way to turn a gas off was to clear it to zero (00/00).
We later added an option, that each gas has an on/off setting. This makes it easier to setup the Predator if you have a set of standard gases, but might not be carrying all of them on a dive. So that existing users wouldn't be forced into using the new on/off settings for each gas, this behavior became an option.
If the "Gas On/Off" setting is set to "Off", then the Predator behaves in the original way (gas must be cleared to 00/00 to turn off). If set to "On", then each gas can be turned on or off. For the newer Petrel product, we found that most divers wanted the on/off setting for each gas, so we removed the option to use both methods.
An important related note is that only gases that will actually be used on a dive should be turned on. The decompression calculations assume that all turned on gases will be used at appropriate depths. If a gas is turned on but never used, then deco predictions will be incorrect (although the final schedule will end up being correct, it is just predictions of future behavior like TTS that will be incorrect).
Also, if you are carrying a gas but don't intend to use it (e.g. a backup gas), then leave it turned off. It is easy to turn a gas on, even during a dive, as a gas is automatically turned on if selected as the active gas. Also, you can turn a gas on without selecting it during a dive by using the "Dive Setup->Define Gas" menu.
Best regards,
Tyler Coen
Shearwater Research
