Spare Speedo is now in Hydra (Fast learning curve that was!). Its all working ok and just needs calibrating. I had a look at this and thought the following was how to do it:

1: Adjust acceleration pot to ensure it doesnt turn when it starts moving
2: Adjust speed pot so it goes in a straight line
3: Adjust deceleration pot so it doesnt turn when it stops

Maybe Im oversimplifying this but any advice would be welcome

Andy