A transition between two states having magnetic or crystallographic structures with a basic lattice and an imposed super-periodicity. In the commensurate (lock-in) state this super-periodicity is a simple rational multiple of the basic @U06562@. In the incommensurate state the ratio of the super-periodicity repeat distance to the basic lattice repeat distance is irrational and may show continuous variation with variation in some degree of freedom (e.g. temperature, pressure, composition) of the system. Example: The transition of Rb₂ZnCl₄ from an incommensurate structure to a commensurate structure at the lock-in temperature, \(T_{\text{L}}\), which is dependent on the crystal growth method and varies in the range \(128\ \text{K}\) to \(190\ \text{K}\).