Speedo Calibration

[everitj]

I have one of the early speedos with the pot on top for fine tuneing.. My speedo is a mile out and I was thinking of trying to calibrate it using my road angel. Has anyone tried this? I was thinking of driving with the dash top off and with the help of a friend trying to get it reading correctly.. Not sure if this is posible but would like to hear from anyone who has tried it...

[harrow_chim]

I did mine using a measured mile (on the M4 near J7) and a stopwatch at 60mph. Took a couple of goes to get it right. I release the clamp behind the speedo and put the dash top back on - I could then just pull the speedo out far enough to get to the pot.
When tested at the top end at Bruntingthorpe it only read 135mph when it was doing top whack of 150mph (according to speed trap set up at end of runway).
Nick