These positions are typically related by symmetry, although there is at least one example of fluoride disorder over three non-equivalent sites in a single cage (SSZ-23, further described below). Both static and dynamic disorder have been found to occur: In the former case, fluoride anions in different unit cells are randomly distributed over the possible positions, but the position of every individual anion does not change over time. In contrast, dynamic disorder implies that the anions move back and forth between the positions. It has to be noted that the ability to distinguish between static and dynamic disorder depends on the observation timescale: For example, "slow" dynamic disorder (i.e., rare movements = long residence times at one position) might not be identified as such with a given method if the related quantity is measured on a shorter timescale. The nature of the disorder can be determined using solid-state NMR methods: