At a given temperature, ${\mathrm{E}}_{\mathrm{cell}}$ changes hence, values of K cannot be measured

${\mathrm{E}}_{\mathrm{cell}}^{\mathrm{o}}$ is easier to calculate as compared to ${\mathrm{E}}_{\mathrm{cell}}$

K also relates with ${\mathrm{E}}_{\mathrm{cell}}$.

${\mathrm{E}}_{\mathrm{cell}}$ becomes zero at equilibrium but ${\mathrm{E}}_{\mathrm{cell}}^{\mathrm{o}}$ does not