Does this help ?

http://www.caigauge.com/documents//product-instructions/spedometers/speedometers/pil042-460-435.pdf

They all read high though as others have said for legal reasons, just live with it.

( except my Lotus Elise that read 6 k lower than I was going, very dodgy in Victoria and South Australia where they use speeding fines to finance the politicians perks smile )

Cheers John
2011 4/4 - "Elrond"
2007 Elfin C3 Clubman - “Gimli”