The evaluation is done in a controlled environment. The vast majority of the police officers working in Canada will never be trained as drug recognition experts. Again, it's a specialized field.
What we do for training is attach an eight-hour block to the standardized field sobriety test course. They're given the general symptomology to be looking for. What they record roadside will in all likelihood be totally different from what I'd see if they brought them back to the office for me to evaluate. Most drugs are short-lived. Some are longer-acting. Some react slowly. Some start their effects very quickly.
So we fully expect that during the evaluation, things will be different from what they saw roadside. Because of that, it's a totality of the evidence right from the time they dealt with the person, from when they walked up to the car, to the conclusion of the evaluation.