As I write in my column today, that buffer or tolerance is 10 per cent, and I've been told about that by two highway patrol chiefs. It's been mentioned to me since then that the buffer does not apply in school zones, although I don't know whether that is the case. On top of the 10 per cent, by the way, is an error allowance of 1kmh for a stationary speed-measuring device, fixed speed cameras among them, and 2kmh for mobile devices.

Now, the new low-level range to come into effect in about six months is one demerit point for exceeding the speed limit by up to and including 10kmh, as opposed to the current three points up to and including 15kmh. My point, then, is that if the buffer is retained this low-level speeding limit will not apply in speed zones of 80kmh and above. That's because in an 80 zone the buffer plus 1kmh margin of error is 89kmh and plus 2kmh margin of error is 90kmh, the latter matching exactly the upper speed of the low-level offence. In 90, 100 and 110 zones the low-level offence is history. Drivers exceeding the speed limit by more than the buffer plus error margin in these zones will go straight into the mid-level speeding bracket, three points thank you very much. Not that they'll get my sympathy, because I see the 10 per cent as generous.

It is 10 per cent because Australian Design Rules for speedos set, for cars made before July 2006, as acceptable a speedo variation of plus or minus 10 per cent of the actual speed. So driving at a speed within that tolerance may be driving to the government's own rules.

Of course fuddy duddy drivers dripping with sanctimony will decry the buffer, or they will until it goes and they're booked for doing 62kmh in a 60 zone.

Another reason for the buffer is that it allows traffic to travel at the speed limit, which traffic controllers and police encourage, without having to be obsessed with the speedo. It is true, too, that many speedos that meet Australian Design Rule requirements do not show increments of 1kmh.

So, should the 10 per cent buffer stay? And if you say not, please tell us if you're often the target of horn-blasting and abuse and why.