Indiana Code 6-2.1-2-2(a) imposes a gross income tax on the receipt of "the taxable gross income derived from activities or businesses or any other sources within Indiana by a taxpayer who is not a resident or domiciliary of Indiana." IND. CODE 6-2.1-2-2(a)(2) To determine whether gross income is derived from an Indiana "source," the Court must: (1) isolate the transaction giving rise to the income ("the critical transaction"). (2) determine whether the Petitioners have a physical presence in, or significant business activities within the taxing state ("business situs"). (3) determine whether the Indiana activities are related to the critical transaction and are more than minimal, not remote or incidental to the total transaction ("tax situs"). First Nat'l Leasing and Fin. Corp. v. Indiana Dep't of State Revenue, 598 N.E.2d 640, 643-44 (Ind. Tax Ct. 1992); Indiana-Kentucky Elec. Corp. v. Indiana Dep't of State Revenue, 598 N.E.2d 647, 663 (Ind. Tax Ct. 1992). The critical transaction is defined as the activity that gives rise to the gross income in dispute. First Nat'l Leasing, 598 N.E.2d at 643. Two tests are used to determine whether income from an intangible has an Indiana source: the "business situs" test and the "commercial domicile" test. See Bethlehem Steel Corp. v. Indiana Dep't of State Revenue, 597 N.E.2d 1327, 1334-35 (Ind. Tax Ct. 1992), aff'd by 639 N.E.2d 264 (Ind. 1994); see also IND. ADMIN. CODE tit. 45, r. 1-1-51 (repealed 1999). Unless a taxpayer is commercially domiciled in Indiana, however, the "commercial domicile" test is irrelevant because the analysis under that test is then identical to the analysis under the "business situs" test. Bethlehem Steel, 597 N.E.2d at 1335 (quoting IND. ADMIN. CODE tit. 45, r. 1-1-51 (repealed 1999)). As this Court has previously held, "the use of the word 'operation' in . . . 45 IAC 1-1-49(6) indicates an active participation in the listed activities of 'ownership, leasing, or rental' is necessary for the establishment of a 'business situs' in Indiana." First Nat'l Leasing, 598 N.E.2d at 644. Indiana determines tax consequences based on the substance, not the form, of a transaction. Bethlehem Steel, 597 N.E.2d at 1331 (citing Monarch Beverage v. Indiana Dep't of State Revenue, 589 N.E.2d 1209, 1215 (Ind. Tax Ct. 1992)). When a taxpayer has more than one "business situs," the Court must determine which is the "tax situs." See Indiana- Kentucky Elec., 598 N.E.2d at 662. . Indiana imposes a tax on every corporation's adjusted gross income derived from sources within Indiana. IND. CODE 6-3-2-1(b). In cases where a corporation derives business income from sources both within and without Indiana, the adjusted gross income derived from sources within the state of Indiana is determined by an apportionment formula. See IND. CODE 6-3-2-2(b). Indiana's apportionment formula multiplies the business income derived from sources both within and without Indiana by a fraction, the numerator of which is a property factor plus a payroll factor plus a sales factor, and the denominator of which is three. Id.