Speedfine calculation?

Coming home from work about 7:30 on Fri night along Beaconsfield parade in Port Melb and passed a speed camera attached to the front of a blue Camry wagon.
Reckon I could have been doing 66km (I glanced at the speedo just as I realised what it was). How do they calculate whether you are over the threshold. Previous fines have been well over so I haven't been in this position before.
Is it :
1) deduct 3 km for camera error allowance and;
2) then if you are >3 km over you get done;
so in a 60km zone your speedo could read 66 and you're in the clear.
I'm looking for some factual information, anyone who wants to tell me to bend over and take it (and there are some of these around), can please piss into the wind.
Thanks,
TopCat

Reckon I could have been doing 66km (I glanced at the speedo just as I realised what it was). How do they calculate whether you are over the threshold. Previous fines have been well over so I haven't been in this position before.
Is it :
1) deduct 3 km for camera error allowance and;
2) then if you are >3 km over you get done;
so in a 60km zone your speedo could read 66 and you're in the clear.
I'm looking for some factual information, anyone who wants to tell me to bend over and take it (and there are some of these around), can please piss into the wind.

Thanks,
TopCat