That's one I'd not heard before!
As for Guzzi speedos, have they improved?

Cheers,

Hi Robbie, the calibration mode is selected by switching on the ignition while simultaneously holding the "trip counter button". After +3 seconds release the button and the speedometer digits will flash. For safety, write down the number you see on the display.
First test the accuracy of the meter, noting the difference between 10 miles on your display and 10 "real" miles on the motorway mileposts. Or time your speed over a set distance and a fixed speed. Then I used the "rule of 3" calculation to get to the correct pulses/mile (might take a couple of changes till you get to the best one, but you can try unlimitedly).
By momentarily pressing and releasing the reset button each number (starting from the left) can be incremented to your calculated value. When the desired value is selected wait a couple of seconds till the next digit will flash, increase this number, etc to the full pulse setting. At the end of the reset, wait another +3 sec for the speedometer to return to normal operation.
Well, this is how it worked for me anyway. Up to you...

Suitcases in the boot of my Aeromax renders my SatNav blind, let alone unreliable!

I’m having an auxiliary receiver added to allow the system to have line of sight to the sky; this should cure my problem.

In a previous car I once had a portable SatNav set up, a Micro Road Pilot hardwired in and, of course, the speedo running. They were all telling me I was going a different speed.

My understanding – and perhaps incorrectly – was that part of the reason the ‘reasonable’ police forces gave motorists the 10% plus 2-3mph leeway when doing speed traps, was to allow for some variance in the calibration of the speedo in the car?

I was told that the law allows for mechanical variance of the speedo of -3% and +10% so permitting your speedo to show (67)70(77).

In my experience pretty much every car I have had shows in the region of +5-10% with some Ford/Vauxhall being even worse. You could also loose a little rolling diameter from under-inflated tyres. My Phaeton shows about 2mph more than the TomTom at 70mph. My Aero shows about 6mph more than my TomTom at 70mph. Ironically I am far more likely to speed in the Phaeton due to the silence and massive torque/autobox/turbos.

In my experience the boys in blue will not look to upset your journey until you are a further 5mph over the real limit or more on the motorway. If you are showing bad road craft or near a known problem area like a school they tend to allow no variance.

I always find it fun if you look at the speed people do through roadworks or as they are passing a police car. Most police sit at 67mph on the motorway to try and reduce bunching so allowing people to make fair progress. You get piles of cars tailing the policeman and then they look at you like you are mad as you gently pass them and make off into the distance.

So if you add all of that up you could see 82 on the clock and still be safe. Then again you could be looking at a ban !