At work we now graph several temperatures in the serverroom (results are not public). We joked (or not..) last Friday that we could add a lot of sensors inside and outside the serverroom (that is where my thinking about 1-wire systems came in again) and have someone research this micro-climate and correlate the micro-climate with the ntp statistics. We did see the influence of the cold wind from the east on the pll stats of several ntp servers.