How to get the zeropoint magnitude?
Magnitude is defined relative to a standard flux of a magnitude 0 object $F_0$.

$$M = -2.5\log(F/F_0)$$

if the error is $F_E$, then $F =F_0\pm F_E$, so the magnitude M is

$$ -2.5\log((F_0+F_E)/F_0) &lt; M &lt;-2.5\log((F_0-F_E)/F_0)$$

The errors here are tiny in comparison to the measured flux, only one part in 10000, so the range of magnitudes is similarly tiny +-0.0001