= Photometric magnitude uncertainty
{title2=$\sigma_m=(2.5/\ln10)(\sigma_f/f)$}
For a fixed <magnitude zero point>, the derivative of $m=-2.5\log_{10}(f/f_0)$ gives the small-error <propagation of uncertainty> formula $\sigma_m=(2.5/\ln10)\sigma_f/f$. A fractional <observed radiative flux> uncertainty of $0.1$ gives about $0.109$ mag of absolute uncertainty. A fractional magnitude uncertainty additionally needs the value of $m$, is undefined at $m=0$, and depends on the adopted <magnitude zero point>.
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