Speedometer jumping, and inaccurate

One thing that i did to solve a jumpy Speedo needle was to pull off the needle & re-coil the little spring. I did this a couple of times, as the first time totally stopped the needle. Th e second time, I loosened the coiled tension a tad, then the needle went 0-60 with no problems. However, I can't attest to the accuracy - I'll check that. BTW, I say '0-60' because I recall somewhere in the past someone telling me that the 'high-speed' on a cordless drill will get you up to 60mph. That has always seemed to be what I've found - so this 'method' may be OK for ball-parking a speed. But, accuracy's different. This usually keeps me from speeding (that + 8mpg).