Is it a cable drive?
My XTZ660 had one of the converters which is fitted between cable and speedo. No stickers, apart from a little one which you put on the glass to obscure the km/h which says mph. It was 100% accurate according to my satnav.
Similar to this, You can probably get them cheaper, but this is the first one I googled http://www.brooksbarn.co.uk/Mechanical-speedo-converter-kph-to-mph_AQQH4.aspx