code: def _to_numeric(self, offset=None, datetime_unit=None, dtype=float):
          
          numeric_array = duck_array_ops.datetime_to_numeric(
              self.data, offset, datetime_unit, dtype)
          return type(self)(self.dims, numeric_array, self._attrs)
docs: A (private) method to convert datetime array to numeric dtype
          See duck_array_ops.datetime_to_numeric