[Alcor]

It’s not dumb, it’s accounting for real world variance in car speedometer accuracy and possible inaccuracies in the measurement process, just because your car is telling you you went 98 or the speed camera is telling you you went 101 doesn’t mean that was the actual speed of your car at the moment.

[craftkiller]

Speed limits are limits, not targets. That's why they're called speed *limits*. You account for variance in the speedometer and the reading device by staying under the limit, not treating it as a target.

[Alcor]

I hope this does not come across as antagonistic but isn’t this then another form of mental math again? "I’m actually not allowed to drive the number on the sign but I’m also not allowed to drive a speed within the margin of error so I could be falsely accused of speeding."

The other way around seems more clear in a legal sense to me because we want to prove with as little doubt as possible that the person actually went above the speed limit. Innocent until proven guilty and all that. So we accept people speeding a little to not falsely convict someone.

[Macha]

So your speedo reads 100 km/h in a 100km/h hour zone. The intention is that you just treat that as a sign that you're at the limit and don't go faster.

Yes, you _could_ do some mental math and figure out that your speedometer is probably calibrated with some buffer room on the side of overreporting your speed, so you're probably actually doing 96km/h and you know you probably won't get dinged if you're dong 105km/h so you "know" you can probably do 110km/h per your speedometer when the sign is 100km/h.

Or you could just not. And that's the intention. The buffers are in there to give people space for mistakes, not as something to rely on to eke 10% more speed out of. And if you start to rely on that buffer and get caught on it, that's on you.

[sokoloff]

As a driver, I control my speed for a variety of factors, but I assume no responsibility for the variance in the speed checking device. That’s on the people deploying them to ensure they’ve done their job (and is part of the reason tickets aren’t issued for 1kph/1mph over in most jurisdictions).