  Electron counting experiments attempt to provide a current of a known number
of electrons per unit time. We propose architectures utilizing a few readily
available electron-pumps or turnstiles with the typical error rates of 100 ppm
with common sensitive electrometers to achieve the desirable accuracy of 1 part
in 10 ppb. This is achieved not by counting all transferred electrons but by
counting only the errors of individual devices; these are less frequent and
therefore readily recognized and accounted for. We thereby ease the route
towards quantum based standards for current and capacitance.
