(a) This account must include the cost of labor, materials used and expenses incurred in connection with sales activities, except merchandising, which are not includible in other sales expense accounts.

(b) This account must include the following labor items:

(1) General clerical and stenographic work not assigned to specific functions.

(2) Special analysis of customer accounts and other statistical work for sales purposes not a part of the regular customer accounting and billing routine.

(3) Miscellaneous labor.

(c) This account must include the following materials and expenses items:

(1) Communication service.

(2) Printing, postage, and office supplies and expenses applicable to sales activities, except those chargeable to account 913, Advertising expenses (§ 367.9130).