The HP 7470 was a small low-cost desktop pen plotter

Plotter

A plotter is a computer printing device for printing vector graphics. In the past, plotters were widely used in applications such as computer-aided design, though they have generally been replaced with wide-format conventional printers...

 introduced by Hewlett Packard's San Diego division. It used a revolutionary "grit wheel" design which moved the paper held in place by a wheel with embedded grit and a pinch roller. The HP 7470 had only two pens, one on either side. It was much less expensive than the previous flatbed design, which was very heavy but had 4 pens. The HP 7475 used a rotating carousel with six pens. That plotter was used in greeting card kiosks. This design was also scaled up for very large pen plotters. These were driven by the HP-GL plotter language which used ASCII

ASCII

The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...

 commands such as PA 300, 4500;PD;

Pen plotters became obsolete with the adoption of ink-jet printers, and processors fast enough to rasterize

Rasterisation

Rasterisation is the task of taking an image described in a vector graphics format and converting it into a raster image for output on a video display or printer, or for storage in a bitmap file format....

 complex images. Houston Instrument and other manufacturers would follow with similar plotters.