61 Pa. Code § 109.7
If the commission for sales made or other compensation for services performed by a nonresident traveling salesman, agent or other employe or casual employe depends directly upon the volume of business transacted by him, his items of income derived from or connected with Commonwealth sources include that proportion of the amount of the items attributable to the business which the volume of business transacted by him within this Commonwealth bears to the total volume of business transacted by him within and without this Commonwealth.
61 Pa. Code § 109.7
The provisions of this §109.7 amended under section 354 of the Tax Reform Code of 1971 (72 P. S. § 7354).
This section cited in 61 Pa. Code § 109.8 (relating to earnings of nonresident employes or casual employes and officers).