It is a defence to a charge under s. 49(1)(f) that at the relevant time the sample was taken, the breath testing instrument was not working properly (see section 49(4)). 

The onus is upon the defence to establish on the balance of probabilities, that at the relevant time of taking the breath sample, the breathalyser was not working properly or had malfunctioned.  Although relevant to the case it is not necessary for the prosecution to prove as an element to an offence under s. 49(1)(b) or s. 49(1)(f) complete compliance with the relevant regulations governing the use of a breath testing instrument: DPP v Luff [2006] VSC 195.