The empirical quantity defined by $$i=\frac{i_{\text{d},l}}{c_{\text{B}}{m}^{\frac{2}{3}}{t}_1^{\frac{1}{6}}}$$ the equation where $i_{\text{d},l}$ = limiting diffusion current, $c_{\text{B}}$ = bulk concentration of the substance B whose reduction or oxidation is responsible for the wave in question, $m$ = average rate of (mass) flow of mercury (or other liquid metal) and $t_1$ = drop time.