As said although you can gauge a rough estimation from the gauge they are by no means accurate at the moment mine tends to hover around the R mark, the fans on mine come on at 88 degrees as I have the standard fan switch and off at 77 degrees, the switch you have is better as the fans come on later but for a much shorter cycle (Hence your gauge showing a high reading), in comparison the standard one brings the fans on to early and for far to long, this is what leads to melting fuses etc!

Martin