An OD, or otonal division, is a kind of arithmetic and monotonic tuning.

Its full specification is n-ODp: n otonal divisions of interval p.

The nth overtone mode, or over-n scale is equivalent to n-ODO. So is n-ADO.

An OD is a specific (rational) type of EFD, or equal frequency division.

example: 4-ODO
quantity 1 2 3 4 5
frequency (f) 4/4 5/4 6/4 7/4 (8/4)
pitch (log₂f) 0.00 0.32 0.58 0.81 (1.00)
length (1/f) 4/4 4/5 4/6 4/7 (4/8)