Abstract: Documents such as checks, food stamps or the like are successively advanced along a path between a transversely spaced pair of light-emitting diodes (LEDs) and a correspondingly spaced pair of photodiodes to generate signals for counting and misfeed detection. Various error detectors detect sheet misfeed by integrating signals derived from one or more sheet sensors and comparing the integrated signal with reference signals that vary with the drive speed. A doubles detector generates a signal indicating a double feed if the integral of an analog optical density while below a predetermined threshold lies beyond a predetermined limit. A potentiometer permits adjustment of the threshold optical density at which the integrator becomes operative. An LED coupled to the output of a spare amplifier on the chain note board permits detection of the momentary presence of an output signal from a particular error detector.