Document reading apparatus, for producing electrical signals representative of information present on a main face of a document, includes feeding means (31), for moving such a document (15) towards a predetermined reading location in the apparatus, and a sensor device (32), disposed at a detecting location upstream of the said reading location, for detecting passage of a leading edge part of the document (15) across the said detecting location towards the said reading location. Optical reading means (11, 12, 13, 14) produce electrical signals representative of such information on that portion of the document (15) which is currently at the said reading location, and control means (21, 22, 23) initiate operation of the reading means upon expiry of a preset delay time after such passage of the said leading edge part across the said detecting location. The apparatus is operable in a calibration mode wherein, when a calibration document (C) bearing predetermined calibration information (3) is fed into the apparatus, such electrical signals derived from the said calibration information (3) are employed by calibration circuitry (21, 23) of the apparatus to measure displacement of the said leading edge part (4) of the calibration document (C) from the said reading location upon expiry of the said preset delay time. The magnitude of the preset delay time is then modified in dependence upon the measurement result. Such calibration can serve to reduce such displacement of the leading edge part of a document read in a subsequent reading operation.