

        Mapping of tick frequencies to multiples allowed for that ticking.
        The default is ::

            self.intervald = {
                YEARLY  : [1, 2, 4, 5, 10, 20, 40, 50, 100, 200, 400, 500,
                           1000, 2000, 4000, 5000, 10000],
                MONTHLY : [1, 2, 3, 4, 6],
                DAILY   : [1, 2, 3, 7, 14, 21],
                HOURLY  : [1, 2, 3, 4, 6, 12],
                MINUTELY: [1, 5, 10, 15, 30],
                SECONDLY: [1, 5, 10, 15, 30],
                MICROSECONDLY: [1, 2, 5, 10, 20, 50, 100, 200, 500,
                                1000, 2000, 5000, 10000, 20000, 50000,
                                100000, 200000, 500000, 1000000],
            }

        where the keys are defined in `dateutil.rrule`.

        The interval is used to specify multiples that are appropriate for
        the frequency of ticking. For instance, every 7 days is sensible
        for daily ticks, but for minutes/seconds, 15 or 30 make sense.

        When customizing, you should only modify the values for the existing
        keys. You should not add or delete entries.

        Example for forcing ticks every 3 hours::

            locator = AutoDateLocator()
            locator.intervald[HOURLY] = [3]  # only show every 3 hours
    Nrõ