I have just installed a SpeedM8 that allows me to calibrate my speedometer to read exactly right.

SpeedM8 Electronic KMH To MPH Converter NCS - Systems

What’s the consensus on what to use as a reference? TomTom OK?

 

Have a word with a friendly local copper and ask for the location of a nearby measured mile. More accurate than a consumer sat nav - and, obviously enough, the same thing the fuzz use.

 

I drive an artic for a living and can safley say that a TomTom IS accurate.
I only know this because the tachograph/speedo has to be calibrated in a wagon as im sure you aware and the TomTom is accurate to the wagon.

 

Cheers for the TomTom words. I hoped as much

I’m sceptical I’d get any decent help from plod.

Me (winds window down) “Hello could you please help me calibrate my speedo”?
Plod (leans into car and sees my CD’s) “Is that home recording? Tut tut. Would you mind stepping out of the car…..”