ALS

An ALS, or arithmetic length sequence, is a kind of arithmetic and monotonic tuning.

shifted undertone series (± frequency) (equivalent to ALS)

(n-)ALSp: (n pitches of an) arithmetic length sequence adding by p

A US is a specific (rational) type of ALS.

The same principles that were just described for frequency are also possible for length: by varying the undertone series step size to some rational number you can produce a utonal sequence (US), and varying it to an irrational number you can produce an arithmetic length sequence (ALS). In other words, by shifting the undertone series by a constant amount of string length, the step sizes remain equal in terms of length, but their relationship in pitch changes.