Hall-plateau voltmeter calibration ($\lambda =I{R}_K/(p{D}_p)$)

For an integer quantum Hall effect plateau with index $p$ carrying a known current $I$, the true transverse voltage is $I{R}_K/p$. If an offset-corrected instrument displays $D_p$, its gain in volts per displayed unit is $\lambda =I{R}_K/(p{D}_p)$. Independent current and displayed-height errors add in relative quadrature. The Hall-bar width cancels; it enters an electric-field calibration instead. A missing plateau height or an unidentified absolute plateau index prevents a unique numerical gain.