Essentially a wrapper to `endpoints`

with the appropriate
period specified; the resulting value derived from counting the
endpoints

As a compromise between simplicity and accuracy, the results will always
round up to the nearest complete period. So n**** - 1 will return
the completed periods.

For finer grain detail one should call
a higher frequency n**** function.

An alternative summary can be found with `periodicity`

and `unclass(periodicity(x))`

.