> int <- ymd("2010-01-01") %--% ymd("2010-06-01")
> dur <- ddays(1)
> per <- months(1)

Interval numerator
==================

> int %/% int
Error: Incompatible classes: <Interval> / <Interval>

> int %/% dur
[1] 151

> int %/% per
[1] 5


Duration numerator
==================

> dur %/% int
Error: Incompatible classes: <Duration> / <Interval>

> dur %/% dur
[1] 1

> dur %/% per
Error: Incompatible classes: <Duration> %/% <Period>


Period numeric
==============

> per %/% int
Error: Incompatible classes: <Period> / <Interval>

> per %/% dur
Error: Incompatible classes: <Period> %/% <Duration>

> per %/% per
[1] 1