Wikipedia:Reference desk/Archives/Science/2024 September 26

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September 26

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Body Roundness Index formula

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Body_roundness_index#Calculation gives the formula

364.2 − 365.5  × √(1 − [waist circumference in cm / 2π]2  /  [0.5 × height in cm]2)

which seems unnecessarily complicated. Why isn't it simply simplified to

  ?

Moreover, as both numerator and denominator have length units, the unit doesn't matter as long as they are the same e.g. cm, mm or inches.

Thanks, cmɢʟeeτaʟκ 04:31, 26 September 2024 (UTC)[reply]

Probaly because the editor who added that didn't know how to render mathematical formulae. You're welcome to change it. Shantavira|feed me 09:16, 26 September 2024 (UTC)[reply]
Thanks. I don't mean the formatting but the division by 2π on top with multiplication by 0.5 below.
Presumably, they meant waist / (2π) instead of (waist / 2)π – BEMDAS is confusing! cmɢʟeeτaʟκ 10:17, 26 September 2024 (UTC)[reply]
Because it's left over from its derivation from the eccentricity formula for an ellipse,  , where the semi-minor axis, b, is the "radius" of the waist and the semi-major axis, a, is half the body height. AlmostReadytoFly (talk) 11:05, 26 September 2024 (UTC)[reply]
Makes sense, thanks! cmɢʟeeτaʟκ 11:34, 26 September 2024 (UTC)[reply]