I've thought about a speedo healer. And was going to get one.

But Kev said that if you heal the speedo, you give the odo reading (which is pretty accurate) a hernia. So, I gave that some extra thinks, and in the interest of knowing where I am re fuel consumption and distance-to-sustenance, I reckon I'll continue with the 10% calculation/correction routine.

Annoying, but simple enough. Interestingly, my small car (a humble Focus ST/XR5, built in Germany) suffers a measly 4% error. Don't know why Yamaha had to be so drastic. Possibly, as as been said, to stop sue-crazy tools from blaming other people for their f&&k-ups.