Bug report: Just press the Bugs button at top of the forum page. Get a separate login there and create a new request once you have verified that it isn't already there.
BTW it is more convenient to add images there, as you can copy regions from SMath canvas and paste them directly in the editor. Much better than here in the forum.

Set the metadata as you feel appropriate, you may have a look how it is done by others.

Units: Do you really want to re-define psi? Does that mean re-definition of lbf or inch depending on geographic location? Anyways, you can insert any expression in the unit placeholder.

I fail to understand the design intent of your example. Once I had to deal with ISA standard atmosphere, but there was nothing like variable pressure units. Just Pa or psi and meters or ft, and K for the temperature, of course.

Let the psi unit be psia and introduce an undefined unit psig with appropriate conversion functions.
This approach prevents you from mixing both types of pressure representations, because you would get a unit mismatch error.
It doesn't, however, prevent you from adding psig values, which might not be a good idea.

All in all this is a conversion very much like between K (absolute) and °C (gauged), just with the nasty difference that the offset isn't constant and has to be specified whenever a conversion is to be done.

psig.sm (6kb) downloaded 21 time(s).