Standing about one meter tall, astromech droids are utility robots designed to perform a large number of duties, most of them associated with mechanical devices and computer systems. These useful work droids are found throughout the galaxy and have been in use for many years. There are several models in production, but the basic design involves a cylindrical body topped by a domed swiveling head. Astromechs move about on two treaded roller legs, and a third, retractable leg is often included for stability. Although they can readily understand some of the common languages spoken throughout the galaxy they communicate verbally through a rapid series of beeps and tones. However, they can also, given the proper connection, produce an on-screen printout in any programmed language. The most common models, known as "R2" units, are equipped with a variety of tools and appendages, which can be interchanged for specific assignments. Common equipment includes a welder, a small circular saw, one or more retractable arms, and a holographic projector. The small robots are often used aboard starships, or "plugged in" to droid sockets on single-pilot fighters such as the Y-wing, the X-wing, or the N-1 Starfighter, where they perform in-flight adjustments and repairs to aid the pilot. Once interfaced with a ship's onboard computer, an astromech can also act as a co-pilot, and perform calculations necessary for a ship to travel through hyperspace.