(a) Each service company must keep its cost allocation system so as to show the nature of each addition to or retirement of service company property, the related total cost, the source or sources of costs, and the property account or accounts to which charged or credited. Records covering jobs of short duration may be cleared monthly.

(b) Each service company must maintain records in which, for each property account, the amounts of the annual additions and retirements are classified so as to show the number and cost of the various record units or retirement units.