wrote

Obviously, this has to be backwards, right? Even so, don't regulations
require cabin air pressure to be between 5,000 and 8,000 equiv.
altitude? Wouldn't that mean one of the numbers they gave me would
have to be between 12.23 psi (5,000) and around 11.0 psi (8,000)?

My experience is based on early jet transports (B-707 B-727) but
should be close for any current jet transport.

The maximum allowable cabin differential pressure was 8.6 PSI which
would permit a sea level cabin up to an airplane altitude of about
22,000'. However, if the final cruising altitude was over 22,000',
the automatic pressure controller would start the cabin "up" shortly
after lift-off. This was to ensure a moderate rate of climb for
passenger comfort...about 300-400 ft/min ROC. At a crusing altitude
of 29,000', the cabin would be at about 3,000' and at 39,000', the
cabin would be at 7,000'.]
At 29,000', the standard day atmospheric pressure is about 4.5 PSI.
Add to that the max differential of 8.6 PSI for a total of 13.1 PSI,
or an equivalent altitude of 3,000'. For 39,000', it would be 2.9
PSI plus 8.6 PSI for 11.5 PSI and an cabin altitude of about 7,500'.

Bob Moore
ATP B-707 B-727
PanAm (retired)