A computer-implemented method for providing performance indicators of destination documents includes identifying a referral document to a destination document, where the referral document comprising a source of at least one visitor to the destination document. The method of this disclosure is specifically useful in animal feed production. Sufficient clearances are thereby secured between electrical conductors in their intersecting portions near their ends where the insulating films are susceptible to damage because of welding heat. Each of the switchable output stages is operative to provide an output that combines the feedforward signal with the amplified communications signal in such a way that the distortion components of the signals at least partially cancel one another. Hence, by applying the voltage thereon, the organic bistable device can be well controlled to be turned on or turned off. A bio-fuel cell system is constituted of the fuel supply body and a bio-fuel cell including electrodes with an oxidation-reduction enzyme present on a surface thereof to supply fuel andor the biocatalyst from the fuel supply body to the bio-fuel cell and also to use the fuel supply body itself as the fuel.