A tattoo machine is a hand-held device generally used to create a tattoo, a permanent marking of the skin with indelible ink. Modern tattoo machines use electromagnetic coils to move an armature bar up and down. Connected to the armature bar is a barred needle grouping that pushes ink into the skin. Tattoo artists generally use the term "machine", pen, or even "iron", to refer to their equipment. The word "gun" is occasionally used but is widely considered derogatory or even offensive by some professional artists. In addition to "coiled" tattoo machines, there are also rotary tattoo machines, which are powered by regulated motors rather than electromagnetic coils. "The basic machine is pretty much unchanged today, in recent years variations of the theme have crept into the market, namely Manfred Kohr’s Rotary machine of 1976 or Carson Hill’s pneumatic machine that uses compressed air rather than electricity, but the principle is essentially the same. "