module CALCULATION_INTERVAL
# A method for calculating the number of sitting days in both Houses during an interval.

We pass the start and end dates of the interval.

  def calculate_sitting_days_in_interval( start_date, end_date )
We set the date to start counting from to the start date.

    date = @start_date
Whilst the date is not later than the end date ...

    while date <= @end_date
If the date is a Commons sitting day ...

      if date.is_commons_actual_sitting_day?
... we increment the Commons sitting day count.

        @commons_sitting_day_count += 1
      end
If the date is a Lords sitting day ...

      if date.is_lords_actual_sitting_day?
... we increment the Lords sitting day count.

        @lords_sitting_day_count += 1
      end
We continue to the **next day**.

      date = date.next_day
    end
  end
end