Very accurate. Have been using it for 3yrs at least cannot remember if the C had it or not but used it all the time on the e. The tyres warm up so in the first few minutes will be around the set fig and on checking with a reasonable guage it tallies. Then it starts rising of course as they get warmer and you will see diferences between axles and on the same axle as well, can be associated with which side is in the sun. It is very variable depending on the weight in the car, the weather, the road etc and aal 4 can change as the trip progresses and circumstances change so one minute the front offiside is lower than the rest then it might go to the same or a tad higher but I have faith in it. What has always exercised my mind is how do they set say the basic pressure ie 280kpa for the EQC when after running the tyres will then have a very variable pressure some times 30 plus more after a longish fast run, what is the allowance they build in. There is probably some formula know to tyre manufacturers. I started taking note after having to replace tyres on the c class which wore very quickly a feature of the car I think. The e was a lot better could have been the tyres pirelli over Hankook of course. Looking at the 6mm when new michelin am already expecting I will have to buy new!