Abstract: Test patterns (6) in bar code of different densities are printed at the start of document (20) preparation on the line with a alignment mark (5). The test patterns (6) are immediately read at different timing intervals (59) corresponding to the densities of the patterns. The highest density pattern (6) having test data which is recognized by the logic (61) as correctly sensed, defines the subsequent printing density to be used. First, the next line of data 3 is printed in the lowest density with a code defining the density of the subsequent printing. When a document (20) is read, the first line is read with the clock (59) intervals corresponding to the lowest density. The frequency is then changed to that defined by the code in the first line. Alternatively, the frequency is adjusted lower when an ordinary line of data is re-read and found to read incorrectly.

Abstract: Alignment mark 5 is printed by printer 30 during the same operation in which bar code 3 is printed. Subsequent alignment is by the optical scanner 32 centering on mark 5. In a specific application a factor relating to the vertical position of scanner 32 to printer 30 is obtained by scanning mark 5 shortly after it is printed. This factor is used to position the scanner 32 to read for errors after a line of code 3 is printed.

Abstract: In a typewriter environment, a carrier mounted sensor for calculating the width of a sheet of paper on the platen and for thereafter setting-up proportional margins for that sheet of paper. In addition to supporting the sensor, the carrier supports the printhead and associated apparatus for detecting the position of the carrier relative to the platen at each escapement position of the carrier. The sensor starts its scan at the extreme left position of the carrier and senses the left edge of the paper at a transition from dark (the platen surface)-to-light (the sheet of paper). This transition point is detected and stored. The carrier continues its rightward scan and the right edge of the sheet of paper signals a transition from light-to-dark. This position is detected and stored. The carrier and sensor continue scanning to the right for a specific distance to eliminate errors that are caused by dark areas on the paper that prematurely trigger light-to-dark transitions.