In the land of Oz, the ADR (Australian design Regulations) allow for a 10% variance in speedo reading to actual speed.
In the past the state police forces have allowed the same 10% variance before booking you. The may well pull you over and have a little chat, but wouldn't book you.
But, in one state (Vic), the Government is enforcing a zero tolerance policy and have made a statutory ruling that only allows for 5% variance.
In NSW the government have amended the law relating to demerit points, which indicates a similar policy to Vic.
1 to 10kmh over the speed limit will attract one demerit point and an $84 fine;
11 to 20kmh over the speed limit will attract three demerit points and a $197 fine;
21 to 30kmh over the speed limit will attract four demerit points and a $338 fine;
31 to 45kmh will result in a three month suspension, five demerit points and a $647 fine;
Over 45kmh will result in a six month suspension, six demerit points and a $1,744 fine.
Here in Washington state, the fines start at 1-5 mph ($27 + court fees) and go up in 5 mph increments up to 40+ over ($182 +cf) - if the speed limit is 40 mph or greater. If the speed limit is 35 or less, it's the same, except 1-5 mph over carries a $37 (+cf) fine and the top of the scale stops at 35+ over ($182 +cf). They manage to toss on enough fees so that no ticket for
anything is under $100 ($101 seems to be a magic number for many minor offenses). Problem is you will rarely ever get a speeding ticket if you're going >20 over the limit, because at that point they can charge you with Reckless Driving instead. That comes with impounding your vehicle and sending you to jail. If convicted, your license is lost for a year, longer if it's not the first time you've been convicted.
On a slightly cheerier note, most officers will give you 5 mph or 10%, whichever is greater, before they'll chase you down for a "performance award." There are a few burgs that are famous for enforcing a zero tolerance and will ticket at 1 mph over.
The county I live in (a small county made up of two islands) is well known for stopping anyone for any reason they can and they'll be zero tolerance if you're not a local resident and just warn you if are a local and the infraction is minor. Our deputies seem to be using this policy primarily for looking for drunks as they seem to find a lot of them based on the police blotters in the local paper. One of their officers on my island (the smaller of the two) holds the state record for the most DUI's written in a year. Pretty amazing for an area with a population of ~10,000 that has no bars, pubs, or taverns, only one restaraunt licensed to serve alcohol and four stores (3 convience and 1 grocery) that can sell beer or wine (you have to go to the mainland to buy hard stuff) - all of which close at 10pm or earlier.
For the record if you loose 12 demerit points you loose you licence.
For how long?