see my zeixtronic gauge reads -16.7 psi normal gauge -15psi my ecu data screen -8 psi so working on what si says about gauge accuracy is right beacause the load points on my ecu start at 0 kpa then the next is -8 (50 kpa) ,and its the second site thats adjusted for idle if i went purely by a gauge which you wouldnt id be mapping the first site at 0 kpa