1. (a) Receipts for services performed by the taxpayer's employees regularly connected with or working out of a New York State office of the taxpayer are allocated to New York State if such services are performed within New York State.
2. (b) When allocating receipts for services performed, it is immaterial where such receipts are payable or where they are actually received.
3. (c) Where services are performed both within and without New York State, the portion of the receipt attributable to services performed within New York State is determined on the basis of the relative value of, or amount of time spent in performance of, such services within New York State, or by some other reasonable method. Full details must be submitted with the taxpayer's return.

Tax Law, § 1454