Va. Code § 58.1-410
Property owned by the corporation shall be valued at its original cost plus the cost of additions and improvements. Property rented by the corporation shall be valued at eight times the annual rental rate paid by the corporation. The value of movable tangible personal property used both within and without the Commonwealth shall be included in the numerator to the extent of its utilization in the Commonwealth. The extent of such utilization shall be determined by multiplying the total value of such property by a fraction, the numerator of which is the number of days of physical location of the property in the Commonwealth during the taxable period and the denominator of which is the number of days of physical location of the property everywhere during the taxable period. The number of days of physical location of the property may be determined on a statistical basis or by such other reasonable method acceptable to the Department.
Va. Code § 58.1-410