The following misinformation has just been posted at the official Bureau website:
My responses to the inaccuracies in this document are prefaced with JM, and inserted herein.
FAST FACTS: How does the Bureau measure temperature?
1. The Bureau measures air temperature using an electronic sensor (a platinum resistance thermistor) placed within a Stevenson Screen, and temperature is recorded every second.
JM: No. The temperature is measured every second, it is not recorded every second by the Bureau. Rather, the Bureau has explicitly stated, most recently in an internal report released just last Thursday, that for each one minute temperature it only records the highest one-second temperature, the lowest one-second temperature, and the last one-second temperature – in that one minute interval. The Bureau does not record every one-second value. In the UK, consistent with World Meteorological Organisation Guidelines, the average temperature for each minute is recorded.
2. The air temperature fluctuates frequently on the scale of seconds. By using a sensor which has a longer response time than the fluctuations of the air temperature, the sensor “averages” these fluctuations.
JM: No. Electronic sensors have shorter response times than mercury thermometers. So, to ensure there is no discontinuity in measurements when the transition occurred from mercury thermometers to electronic probes the maximum and minimum values need to be calculated from one-second readings that have been averaged over at least one minute.
3. Both the mercury-in-glass thermometers, and the electronic sensors, are housed within a Stevenson Screen. The time taken for air to be exchanged from the outside environment to within the screen provides a further time integration for the measurement of the ambient air temperature.