Speedo calibration

Hi , is it possible to replace some part of the speedo drive so as to get a more accurate reading on the dial? I was wondering as I have a doodad on my phone that gives me a gps speed and when keeping with traffic on the motorway it says 70 but the dial is saying 74 or 75. The dial is also off when compared to those roadside speed signs both the ones that go off if you are too fast and the other ones that give a specific speed. I know it's illegal to have a speedo that indicates a lower speed than you are traveling and that the construction and use regs state the difference can be as much as 10% lower than actual but i was hoping that like on a land rover there's a range of different drive gears that can be used to tighten the tolerance between actual speed and indicated? I don't need different size tyres either. Any help?

Are you still running a standard transfer box? Or a 410 / lobster, etc...

Standard box kit -

www.auszookers.com/forum/viewtopic.php?f=5&t=32176

Electrickery circuit to change the number of pulses from the speedo pickup...

'lobster, etc -



"just" a matter of getting the speedo cog with the right number of teeth...

Tippex on the speedo.

Ok so a kit is available. I will look into it cheers.