Abstract: For controlling the acquisition of data in an optical character recognition system having a head for scanning characters, a guide is provided to be disposed along the series of characters. A rail on the guide cooperates with a groove in the head to guide the head along the characters. Disposed on the guide is a reticle having a saw-toothed pattern with segments at 45.degree. with respect to the rail. A linear sensor array, attached to the head normal to the groove monitors the position of points of the reticle normal to the track. This normal position is then translated to the position of the head. Every time the head moves a predetermined distance, it is caused to output data relating to the series of characters. The invention can also be employed to monitor position in any system having an element that moves along a path.