Comment 9 for bug 1092970

The patch also contains one significant bugfix. When iMac is not used and all temperature dropped down, some sensors become unreliable and it can happen that reported temperature is -1 C, which is really high number if read as a signed integer from a file. Then your fans are running at their maximum speed so it seems your mac is flying to the moon.

These sensors report temperature 0 C and are useless for counting average temperature. So bugfix is that any sensors which report value lower than 5 are excluded.