The supervision and engineering includible in the operating expense accounts shall consist of the pay and expenses (company and railroad transportation, lodging, meals, taxi and car fares and other traveling and incidental expenses) of superintendents, engineers, clerks, other employees and consultants engaged in supervising and directing the operations and maintenace of each steam utility function; also office supplies and expenses, including the maintenance of office furniture and equipment. Whenever allocations are necessary in order to arrive at the amount to be included in any account, the method and basis of allocation shall be preserved.