For the purposes of Part 9 of the Act, a digital toll camera unit is used in the prescribed manner if—
(a) it is positioned so that the digital toll camera unit takes images of the registration numbers of vehicles driven in the toll zone and transmits the images taken to a control unit; and
(b) it has been tested in the manner set out in regulation 13; and
(c) it is tested at the following times—
(i) in the case of a digital toll camera unit that has been repaired or modified, after the repairs or modifications are made and before the occasion of the digital toll camera unit's first use after the repairs or modifications; and
(ii) in any case, within a period of 24 months before the occasion of its use.