Sec.  36.373   Services—Account 6620.

   (a) For apportionment purposes, the expenses in this account are first
   segregated on the basis of an analysis of job functions into the following
   classifications: Telephone operator services: publishing directory listing;
   and all other.

   (1)  Expenses  may  be  apportioned among the operations for groups of
   exchanges. A group of exchanges may include all exchanges in the study area.