Where the proof of the commission of an offence under this Act involves the proof of the speed at which a person (whether the accused or another person) was driving -
(a) the uncorroborated evidence of one witness stating his opinion as to that speed shall not be accepted as proof of that speed,
(b) the onus of establishing that speed prima facie may be discharged by tendering evidence of indications from which that speed can be inferred which were given by a watch or electronic or other apparatus (including photographic apparatus), and it shall not be necessary to prove that the watch or electronic or other apparatus was accurate or in good working order.