= Magnetic field from a Zeeman diagram
{title2=$B=3s_E/(2\mu_B)$}
For weak-field sodium D lines neglecting <hyperfine structure>, the smallest adjacent spectral spacing in the full electronic pattern is $s_E=2\mu_BB/3$. A drawing without a labelled <energy> axis can still estimate $B$ if it includes both unsplit D lines with known <wavelengths>: their separation calibrates $hc(1/\lambda_2-1/\lambda_1)$. Divide the drawn split spacing by the drawn unsplit separation before using that <energy> scale. Graphical line thickness, unequal drawn spacings and uncalibrated rendering limit precision; they do not justify exact numerical field values.
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