For example, if I know the mass of a planet and the distance of its satellite from it, I can tell with certainty the period of the revolution of the latter according to Kepler's second law.
Adibidez, planeta baten masa eta bere satelitearekiko distantzia ezagutzen badut, orduan ziurtasunez ondoriozta dezaket bira emateko behar duen denbora, Keplerren bigarren legearen arabera: