Concepts -------- time-series ^^^^^^^^^^^ A time series is an xarray or pandas ..__time_interval Intervals ^^^^^^^^^ Intervals in vtools are equivalent to `freq` arguments in Pandas. In some cases strings or timeDelta objects can be used, but the one that behaves best in math operations and the main implementation class in Pandas is the `Offset `_ class. One way to construct intervals quickly are the :func:`vtools.seconds` :func:`vtools.minutes` etc convenience functions.