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Definitions of psi and pound_force_per_square_inch differ #499

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lysogeny opened this issue Jan 8, 2025 · 1 comment
Open

Definitions of psi and pound_force_per_square_inch differ #499

lysogeny opened this issue Jan 8, 2025 · 1 comment

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@lysogeny
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lysogeny commented Jan 8, 2025

Greetings!

Nice project, fun to work with!

I was recently working with some of the pressure units and noticed that the definitions for psi and pound_force_per_square_inch differ. Is this intentional? I thought these should just be synonymous. The latter seems to have much more precision.

@psi: 6.894_757_E3; "psi", "pound-force per square inch", "pounds-force per square inch";

@pound_force_per_square_inch: 6.894_757_889_515_779_E3; "lbf/in²",

@lysogeny lysogeny changed the title Definitions of psi and pound_force_per_square_inch Definitions of psi and pound_force_per_square_inch differ Jan 8, 2025
@iliekturtles
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After some digging I'm not sure the exact reason both definitions exist. There wasn't any discussion about it in #79 and I'm guessing that because NIST has both listed we added both. The duplication may also be to allow for both the lbf/in² and psi abbreviations.

Note that in NIST 811 appendix B.9 neither entry is exact (not in bold face) and is limited by significant figures. pound_force_per_square_inch is included in the test at the bottom of the file which compares against the derived conversion factor using pound_force and square_inch. psi isn't explicitly tested.

I'll leave the issue open as something like the following should be done:

  • Clarify/document the duplication, ensure there is consistent guidance to follow if the issue arises for other units.
  • Add psi to tests.
  • Use the same conversion for both entries.
  • Handle significant figures in tests?

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