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- Interline Space (IS, is, Is): 1 IS the the distance between two staff lines, or more exactly, the distance between the vertical centers of two adjacent staff lines. This unit allows to measure distances within a staff, independent of the actual staff size. IS is both used to measure vertical and horizontal distances.
- Line Position (LP, lp, Lp): Independent of the number of lines of a staff, LP 0 is always on the bottommost line. LP 1 is a half IS above (in the center between the two bottommost staff lines), LP 2 is on the second staff line from below, and so on. For positions below the bottommost line, negative values are used. For example, LP -2 is the first position where a note would need a leger line.
In the source code, the units are often used at the end of variable names. For example, xMm is a horizontal position in mm, offsetIs is some offset in interline spaces and noteLp is the line position of a note.