Fast & Slow Scan Directions
In inkjets with moving carriages, the "fast scan" is the direction of the relative movement of the head and substrate. The "slow scan" direction is at 90 degrees to the fast one. These terms are useful when relating the printing motion to a particular image. Single-pass inkjets (such as digital label presses and web fed commercial inkjets) also have different characteristics for the print width and the length (ie the direction that the media travels in), as the width resolution is constant while the length varies with the speed that the media is fed under the heads.