Scroll up and down using the UP and DOWN buttons. Pressing SELECT when the Primary Mix or ADD is highlighted will open the Add/ Edit Gas Screen. Pressing SELECT when an Additional Mix is highlighted will bring up a pop-up menu with options to Edit, Remove, or (in the case of the Additional Mixes) to make the selected mix the Primary.
Choosing Edit or the Add option will open the Add/ Edit Gas Mix screen where the gas mixture and tank size can be defined.
If you frequently dive with a standard EAN/ Nitrox mix, or even just different tank sizes, this screen allows you to quickly switch your primary gas without having to enter all the details each time.