The Aroon oscillator is made of the difference between the Aroon Up and the Aroon Down curves. Aroon Up and Down represent the number of days since the most recent x-period high for Aroon Up and x-period low for Aroon Down.
coded by request on forums.
// parameters
// N = 100
up = AroonUp[N]
dn = AroonDown[N]
AroonOscillator = up-dn
RETURN AroonOscillator, 0 as "mid-level", -70 as "low-level", 70 as "high-level"