Observation run = you get a set of directions and clues and you have to follow those directions exactly with no back tracking answering the questions.
Usually done with a passenger and the car that can answer the most questions is the winner for the day.
Usually start in the morning going around adelaide and then head into the hills somewhere to end up at a park for a bbq lunch and then back down through the hills to adelaide for the results. Something like this anyway, and they are a heap of fun as you are trying to spot billboards, signs and all sorts of stuff according to the clues. Oh yeah i forgot to say that cars are let off at about 15 minute intervals to stop people following each other.