IMyAirVent.GetOxygenLevel

In Testing
Creative, Earth-Like -200m sealevel:
Large Grid returns 0.90
Small Grid returns 7.2

Moved both up to 3000m sealevel:
Large Grid returns 0.90
Small grid returns 7.2
? ? ? ?
add/remove a block from both large grid and small grid
Large Grid returns 0.7131
Small Grid returns 6.267


So it appears unless a door opens or closes or a block added or removed, the grids do not update GetOxygenLevel
GetOxygenLevel returns 0-1 with 0.5 is 50%
Small grid returns well above the upper limit...

IMyAirVent.GetOxygenLevel