OK, what it's showing is that as temperature increases so does the fan RPM. This means that the hotter it is the more the fan will cool the player. When I ran the test I covered up the vent holes so that the temp would climb nicely and whenever the temp indicated by Hijack (thanks Mark ) increased by another degree C I would take a reading of fan RPM. This at least proved to me that the circuit worked over the kind of temperature range that I need. I'd like to do some tests over a larger temp range and see if I can increase the rate of change of fan speed against temperature. It seems to work very well but it's early days and I still need to take it on a longish run to see how it performs in the car.

Hope this clarifies things a bit .