Section 28

Where in the case of any trade, business, profession, vocation or employment, it is necessary in order to arrive at the income of any year of assessment or other period to divide and apportion to specific periods the income of any period for which accounts have been made up, or to aggregate such income or any apportioned parts thereof, it shall be lawful to make such a division and apportionment or aggregation, and any apportionment under this section shall be made in proportion to the number of days in the respective periods, unless the Collector having regard to any special circumstances, otherwise directs.