By default, Suunto EON Steel has only one gas (air). You can modify O2 percentage and pO2 settings in the Gases menu.
You need to define all gas mixtures intended to use during the dive in the Gases menu in order that the decompression algorithm works properly.
If you need more than one gas, activate multi-gas option in the device menu under Dive settings » Parameters.
If you want to use trimix gas mixtures (with helium activated), you need to turn helium on under Dive settings » Parameters. When this is done, you can change helium percentage (He%) for selected gas in the Gases menu.
You can activate multi-gas diving and helium, configure dive modes and change gas settings using Suunto app, too.
When you have analyzed your gas, you should round the result down when entering it for Suunto EON Steel. For example, if the analyzed gas is 31.8% oxygen, then define the gas as 31%. This makes the decompression calculations more conservative.
If you need to adjust the computer to provide more conservative calculations, use the personal adjustment feature to affect decompression calculations or reduce the pO2 setting to affect oxygen exposure according to the entered O2% and pO2 values.
THE DIVE COMPUTER WILL NOT ACCEPT FRACTIONAL PERCENTAGE VALUES OF OXYGEN CONCENTRATION. DO NOT ROUND UP FRACTIONAL PERCENTAGES! Rounding up will cause nitrogen percentages to be understated and will affect decompression calculations.
You can customize what you see in the Gases menu using the Suunto app.
It is important to understand how the Gases menu works when multiple gases and helium are activated. For example, you may have the following gases when diving to 55 m (180.5 ft):
In the screenshot below, the menu has three gases and tx18/45 is selected as the active gas. Even though only one gas is active, the decompression algorithm calculates ascent time (during dive) using all these three gases.
To select another active gas before diving:
If you are diving with only one gas, ensure you have only that one gas in the Gases menu. Otherwise, Suunto EON Steel expects you to use all gases in the list and notifies you to change gases during the dive.
When you select CCR mode, gas mixtures are divided to open-circuit and closed-circuit gases. See Rebreather diving.