SLING, by Ole Kirkeby, is an acronym for “Schoenberg-Lyrebird Isomorphic Notation for Guitar.” It is closely related to Lyrebird by Jan Braunstein, Clairnote by Paul Morris, and MSG by Ole Kirkeby. Staff lines, from bottom to top, are E2 – C3 – E3 – C4. The notation is designed for the major-thirds tuning for six-string guitar, in which the pitches of the strings are, from bottom to top, E2 – Ab2 – C3 – E3 – Ab3 – C4. Kirkeby maintains a web site with information about how to play a guitar tuned in major thirds.
A Lilypond file for the above 3-octave example is provided. (See LilyPond.) The file requires a Lilypond template for Lyrebird and another for MSG to be present as well.