Yeah I used one when I was racing. Was helpful and interesting in equal measure, though I didn't race often enough to build up a decent data base for my setup.

Still have it in the kitchen and glance at it ever morning to see just how bloody cold it'll be outside...
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball