Notation in fluid dynamics: A circle with a horizontal bar inside

[Leo Liu]

Homework Statement

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Relevant Equations

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I came across this notation when reading the wiki article on Venturi effect, which baffled me. Can someone please tell me its meaning?

 

[phystro]

It is actually explained in a confusing way. The act of pressure measurement itself is interfering with the actual values of temperature T, pressure P, molar mass Μ, density ρ and concentration C of the liquid. Hence these physical quantities around the pressure-based meter have different values which are denoted with this "funny" notation.

 

[haruspex]

I assume the article is https://en.m.wikipedia.org/wiki/Venturi_effect.
Se if this article oriented more towards engineers helps:
https://instrumentationtools.com/pressure-temperature-compensation/