Yes, we know that your speedo is 10% out
Strom speedos on average appear to read 10% faster than the actual speed being travelled.
If you use the Google search button in the centre of the screen with the string "speedo error" you will find hundreds of posts on the subject with various suggested remedies and explanations.
We do not need another speedo error thread just for the sake of bitching about something that most people know about so let your fingers do the walking before you start one.
All threads on this topic started after today that are simply bitching will be instantly deleted.