were landscape-format pages of 14 × 8½ inches (legal size), allowing for 132 columns by 66 lines (at 8 LPI) on a more compact page. These continuous forms were advanced through the printer by means of tractors (sprockets or sprocket belts). Depending on the sophistication of the printer, there might simply be two tractors at the top of the printer (pulling the paper) or tractors at the top and bottom (thereby maintaining paper tension within the printer). The horizontal position of the tractors was usually adjustable to accommodate different forms. The earliest printers by IBM used a hydraulic motor to move the forms. In later line printers, high-speed servomechanisms usually drove the tractors, allowing very rapid positioning of the paper, both for advancing line-by-line and slewing to the top of the next form. The faster line printers, of necessity, also used "stackers" to re-fold and stack the fan-fold forms as they emerged from the printer. The high-speed motion of the paper often developed large electrostatic charges. Line printers frequently used a variety of discharge brushes and active (corona discharge-based) static eliminators to discharge these accumulated charges. Many printers supported ASA carriage control characters which provided a limited degree of control over the paper, by specifying how far to advance the paper between printed lines. Various means of providing vertical tabulation were provided, ranging from a paper carriage control tape loop to fully electronic (software-controllable) tab simulation. Origins Tabulators built by the U.S. Census Bureau for the 1910 census could print their results. Prior to that, tabulator operators had to write down totals from counter wheels onto tally sheets. IBM developed a series of printing accounting machines, beginning in 1920. The 285 Numeric Printing Tabulator could read 150 cards per minute. The 405, introduced in 1934, could print at 80 lines per minute. It had 88 type bars, one for each print position, with 43 alphanumeric bars on the left, followed by 45 numeric-only bars. The IBM 402 series, introduced after World War II, had a similar print arrangement and was used by IBM in early computing devices, including the IBM Card-Programmed Electronic Calculator. IBM's first commercial computer, the IBM 701, introduced in 1952, used a line printer, the IBM 716, that was based on the type wheel IBM 407 accounting machine. The 716 was incorporated in subsequent mainstream computers in the IBM 700/7000 series. An early drum printer was the