In musical set theory, an interval vector (also called an interval-class vector or ic vector) is an array that expresses the intervallic content of a pitch-class set. Often referred to as a PIC vector (or pitch-class interval vector), Michiel Schuijer suggests that APIC vector (or absolute pitch-class interval vector) is more accurate. Interval class 0, representing unisons and octaves, is omitted. A scale whose interval vector has six unique digits is said to have the deep scale property. Major, natural minor and modal scales have this property.