primitive tunes on these printers by timing the nonsense of the printout to the sequence on the chain, a rather primitive piano. IBM was probably the best-known chain printer manufacturer and the IBM 1403 is probably the most famous example of a chain printer. Train printer Train printers place the type on a horizontally-moving circular train of print slugs. with multiple characters per slug, on a track, The technology is almost identical to print chains. Band printer Band printers are a variation of chain printers in which a thin steel band is used instead of a chain, with the characters embossed or etched onto the band. Again, a selection of different bands are generally available with a different mix of characters so a character set best matched to the characters commonly printed can be chosen. Dataproducts was a well known manufacturer of band printers, with their B300, B600, and B1000 range, the model number representing the lines per minute rate of the printer. (The B300 is effectively a B600 with only half the number of hammers—one per two character positions. The hammer bank moves back and forth one character position, increasing the average number of band movements required for each line.) Bar printer Bar printers were similar to chain printers but were slower and less expensive. Rather than a chain moving continuously in one direction, the characters were on fingers mounted on a bar that moved left-to-right and then right-to-left in front of the paper. An example was the IBM 1443. Common characteristics In all three designs, timing of the hammers (the so-called "flight time") was critical, and was adjustable as part of the servicing of the printer. For drum printers, incorrect timing of the hammer resulted in printed lines that wandered vertically, albeit with characters correctly aligned horizontally in their columns. For train and bar printers, incorrect timing of the hammers resulted in characters shifting horizontally, printed closer or farther from the next character, albeit on vertically-level printed lines. The vertical misalignment of drum printers is more noticeable and annoying to human vision (see the sample pictured in this article). Most drum, chain, and bar printers were capable of printing up to 132 columns, but a few designs could only print 80 columns and some other designs as many as 160 columns. Comb printer Comb printers, also called line matrix printers, printed a matrix of dots instead of individual