Hi all. I'm trying to set up my zf6 in a barra car in Australia. I have noticed the vehicle speed indicated on the scanner is about 10% faster than my gps speed. I'd like to adjust this to be accurate before I start tuning shift points etc. No matter what I do on the "speedo" settings the scanner will display 10% error, diff ration and rpm/km make no difference. Is there another way to make the ecu speed read 10% lower than it is?

Thanks