1. A reference to the ancient method of writing in which the lines are inscribed alternately from right to left and from left to right.
2. Having a back-and-forth motion with a small step at right angles to the transit at each pass, as in a scanning device.
3. Etymology: turning like oxen in ploughing; a term used only in early Greek writing, which went from left to right and then right to left alternately.

Scanning in which the detector that records isotopic emissions moves in alternating opposite directions in a descending series of horizontal lines.