(3)No person shall be Convicted of an offence punishable under sub-section (1) solely on the evidence of one witness to, the effect that in the opinion of the witness such person was driving at a speed which was unlawful, unless that opinion is shown to be based on an estimate obtained by the use of some mechanical [* * *] [The word 'timing' omitted by Act 100 of 1956, section 86 (w.e.f. 16-2-1957).] device.
