Speedometer accuracy

[Wheezybiker]

Other than being pulled over by a copper is there any other way of checking speedo accuracy

Is it done on mot or any other service or inspection

And also where do you stand with the law though I suspect I already know the answer to that one

Many thanks

[Copycat73]

a gps. ie sat-nav or smartphone app..
most over read by +9%
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[TheSmiler]

What about the 30 limit signs I've been told before that they are pretty much 99% accurate before. That was a on a speeding course.
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[Falco]

As Copycat says, GPS is easiest (though still not super accurate).

As for the law, I think you get 2mph over no questions asked. After that it is 10% of the posted limit + the 2mph (30 zone = (2+3) 35, 70 zone = (2 +7) 79. Technically prosecutable but generally ignored unless you are particular egregious (or officer in question is having a bad day).
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I tell you what, mathematically, I'm having it

[Copycat73]

[Howling Terror]

Those 30 limit signs are way off at 150mph.
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[Copycat73]

[andyscooter]

[Wheezybiker]

Thanks for the answers will go find a speed awareness sign and try several passes maybe get an idea of how accurate mine is

[Matt B]

[ThatDippyTwat]

[Qyburn]

[Wafer_Thin_Ham]