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    "ISO 21748: u = √(s_L² + s_r²/n) of a mean of n replicates from stated precision components. n≥2.",
    "s_r and s_L are ≥ 0. Both zero is valid (u = 0).",
    "Not R = 2.8·s_R, not Type A from a sample, and not U = k·u."
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    "Does not compute expanded U = k·u"
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    "negative s_r or s_L → VALUE_OUT_OF_RANGE",
    "s_L = 0 is valid"
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