Nomen Nescio writes:

My wris****ch has an altimeter. I know EXACTLY what cabin pressure
is.

Then you know that all airlines are not flying with cabin pressures of 5000
feet. The cabin pressure depends on the aircraft's altitude, the maximum
pressure differential for the aircraft and any climb or descent in progress.

I've never seen it. Lowest I've seen is 5000 ft. Normal seems to run about
5500. Assuming a 30k+ altitude.

Don't assume a 30K+ altitude. Many flights take place below that.

Never used except in an emergency.

That's not what the FARs say.

Irrelevant.

Highly relevant when the major effect of hypoxia is visual impairment.

If you're a fat smoker in poor cardio-vascular health, you may notice a
difference.

A lot of pilots in good health notice a difference when they take oxygen at
5000 feet or above. But don't worry, it's not illegal to skip the oxygen at
5000 feet even though it may cause visual impairment, just as it's not illegal
to smoke even though it may cause cancer.

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