Hello again LGN1,
You're welcome...and thank you.
Personally, I would prefer the CO2 model. Within the context of "realism" and given the limitations of the game engine, it would seem to be the closest method of capturing the "feel" of how things were done in a practical manner back then.
On the other hand, how would the problem of limiting the submerged endurance due to CO2 build-up be reconciled with the ability to extend that limit? The CO2 content could be allowed to increase to an unrealistic level of 4% before using absorbent or adding "anti-CO2". Would you still be able to label that absorbent/"anti-CO2" as an O2 Supply and display that on the gauges? There's no doubt that having a "CO2 Gauge" is not realistic for the technology available at that time; the LI's text report of CO2 level is quite correct and completely adequate IMHO.
As I mentioned, the messages were "annoying", in that I (as the CO/KL) would expect to get regular reports on the CO2 level and/or the presence of any other unwanted gases in the boat (CO, H2S, NOX, SOX, CL2/chlorides, etc.), but would seldom expect to get a report on just the O2 content. So, if a bigger, better fix is not workable, the changes I made to the messages will suit my personal tastes.
BTW, I made another little change to the "en.menu" text reports to suit my own experiences at sea. Lines 4814 and 4818 became "Visibility is improving, Herr Kaleun" and "Visibility is deteriorating, Herr Kaleun".
Warm regards; sink 'em all!
