= Locked-mass and returned-mass yield conventions
{title2=$y=bR/(1-R)$}
Let a fraction $R$ of gross stellar birth <mass> return immediately, and let the new metal source be $bR\Psi$. The yield per permanently locked <mass> is then $y=bR/(1-R)$. Metal conservation in an initially pristine closed box gives $Z=y\ln(M_0/M_g)$. A coefficient defined by the metal source must not be confused with a yield normalized per locked stellar <mass>; the source convention must be stated, especially when taking $R\to0$ or $R\to1$ limits.
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