Error expressions derived from the commonly used equations of electroanalytical chemistry using Taylor's series show how a calculated value of n, the number of electrons transferred, depends on the error in D, the diffusion coefficient. The error relationships for chronoamperometry, polarography, chronopotentiometry, and voltammetry at stationary and rotated-disk electrodes are given. It is found that when the relative error in D is less than 10% a simple linear relationship between the error in D and n is a satisfactory approximation.