Not sure how to post this on the bug reporting tracking list

1. Options decimals does not carry over within an equation where we use the equal sign at the end
   
2. psi is actually psig or psi(g) and should be relabeled in the drop down box

BUG.smz (3 КиБ) скачан 54 раз(а).

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.

I thought I was clear. Compressed air is my example and I used Denver @ elevation 5200 ft. 1 atmosphere in Denver is 12.2 psig not 14.7 psig so 1 atmosphere is relative to the elevation. When you work any math out, we should be using absolute values. With temperature, it's better defined and we have deltaF or deltaC for ease of use in formulas.
All math is in terms of pisa and I need to convert psig

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 (5 КиБ) скачан 36 раз(а).

Wrote

I thought I was clear.
Compressed air is my example and I used Denver @ elevation 5200 ft.
1 atmosphere in Denver is 12.2 psig not 14.7 psig so 1 atmosphere is relative to the elevation.
When you work any math out, we should be using absolute values.With temperature,
it's better defined and we have deltaF or deltaC for ease of use in formulas.
All math is in terms of pisa and I need to convert psig

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The point you missed is that ISA defines Air @ "Standard Temperature vs altitude"
From recollection, this standard temperature is taken up to 11 km [-56.5 °C].
It is linear from sea level [visit Wikipedia ...]
The region around 11 km [Tropopause] is unstable.
Then, you have to correct for you local day by day °C.
Mexico city is ~ 4 km altitude ... some Incas leave up to 7 km altitude.