Speedometer adjustment

Is there a way to adjust the standard speedometer, mine is consitantly about + 10 miles an hour off. I have checked the speedo drive and it is the 15/12 ratio.

These Smiths magnetic speedos (and tachos too) can be adusted by a screw but it is inside and you need the right equipment to remove and then replace the chrome rim so you will need to send it to one of the reconditioners such as Nisonger at 570 Mamaroneck, Mamaroneck, NY l0543..attn: Bob Castagnetta , Phone 9l4 38l-l952 . If it is a Veglia Speedo, sorry but just throw it away and get a smiths.

Another option is to buy a pushbike electronic speedo and use that to show your true speed(they are calibrated by programing them with the wheel dimensions) and keep the speedo for originality.