mechanical speedo calibration

["----> Bob" <mx@snet.net>]

Part II of my 4000Q speedo issues. 
I replaced the speedo cable, and now the speedo reads EXACTLY 10mph
faster than actual.

Exactly.   (verified with rally computer)

How did it get this way? My guess is that when I had the speedo apart to
fix the odo, I put the needle back wrong.  However, what I did was to
lift the needle off of the rest pin and let it float. I then marked that
position (while having it flat on the table). I reassembled it in
exactly that place. So what went wrong?
How do I calibrate it now?

Thanks
Bob