How acurate are the advisory speed traps?

[Louwai]

The speed traps should be accurate,

Dunno about that,
I came thru the one on the Western both directions.
I was doing the same speed on the car speedo both times & the "advisory " speed was different.
Sitting on 120 on the car speedo. The advisory going to Ballarat was 112klm. On the way back it said 118klm