Approaching one of those trailers setups that read your speed the other day so I sat the fes on exactly 80 kliks and guess what? It showed my speed as only 75k. So at an indicated 100k its only doing about 94k. No wonder when I set the cruise to 100 kliks all the traffic is passing me. So it looks like i need to set it to 107kliks to be at the 100 speed limit. You would think that in this day and age a new car speedo could be made more accurate than that.
I also checked the capri speedo on the same day and for80k on the speedo it said speed was 79k. How come an old cable speedo can be so accurate and modern electronics so far out?

I noticed the same in my WT Fiesta when comparing the speedo to the GPS which is supposed to be more accurate. The speedo is reading 100kph when the GPS says i'm doing 92 and at 110kph i'm doing 100........... the only answer is to speed up to what the GPS is stating. From other forums this is fairly common and manufacturers are allowed this sort of margin below actual speed and not above..............

in the wifes toyota with the GPS the gap appears to increase the faster you go i.e. the speedo is almost spot on at 40 k's but close to 10 k's out at 100 k's

Is the GPS really that accurate though?

It appears to be closer to the mark when you go through a speed display thing on the side of the road