I installed Temperature Gauge onto my rMBP and noticed that the fan RPM is reading 0 at 53C. I'm just browsing the web on Safari, using email and have Living Earth, Radar Live Pro, Temperature Gauge, and Memory Monitor running in the background. It isn't a high workload for the machine. I know the fan kicks up really loud when I'm playing Civilization 5 on it. Is this normal for the fan to be off completely?