Think you have that wrong. Sat navs generally under-read your speed. I know this because in a brand new BMW (where you would imagine the speedo to be accurate) my sat nav always shows about 3 or 4mph less than the speedo. Therefore it follows that if you rely on the sat nav, when it shows you are doing 30 you are more likely to be doing 33!! I reckon you have an accurate speedo in that Astra!Best solution, well one solution, if you have a smartphone or a satnav is to use that, my one year old Astra shows 70 on cruise, satnav says 67, better to be under than over (!!).
Mick
Think you have that wrong. Sat navs generally under-read your speed. I know this because in a brand new BMW (where you would imagine the speedo to be accurate) my sat nav always shows about 3 or 4mph less than the speedo. Therefore it follows that if you rely on the sat nav, when it shows you are doing 30 you are more likely to be doing 33!! I reckon you have an accurate speedo in that Astra!