|WTT User's Guide|
|ρ = MW/vm|
|z = pvm/RgasT = 1 + B/vm + C/vm2|
|B = ∑bi/Ti, i ∈ [0, nterms - 1]|
|C = ∑ci/Ti, i ∈ [0, nterms - 1]|
where z = compressibility, MW = molar mass, Rgas = universal gas constant and vm = molar volume
The basis for this functional form is discussed in  and .
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The TRC Group is part of the Thermophysical Properties Division in NIST's Material Measurement Laboratory
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