b. having units of the same dimensions and being related by whole numbers
(kŏ-men -shŭ-ră-băl) Denoting orbital periods that are in rational proportion, i.e. in which one is a simple fraction (one-half, one-quarter, two-thirds, etc.) of the other. The condition is described as a commensurability. It is observed, for instance, between the orbital periods of planets (e.g. Neptune : Pluto is 2:3), and satellites (e.g. Io : Europa is 1:2). Commensurabilities arise from the effects of resonance.