Average temperature

The average temperature for the day, as recorded in the dayfile.txt, is calculated by Cumulus using samples of the temperature taken at 1-minute intervals (sometimes called the 'integration method'). (This assumes Cumulus is running continuously, if it has just been restarted, for some station types Cumulus will use the temperatures stored at the console logging interval for the period since Cumulus previously ran). Each minute the new measurement is added onto the accumulator Total and increments by one the counter Samples in the today.ini log file. At rollover, the AvgTemp field in yesterday.ini holds the final integrated mean calculated by the quotient of Total over Samples in the old today.ini.

This offers an alternative to the simple mean of the highest and lowest temperatures of the day, and can give a 'better' average in cases where the high or low temperature occurred for a relatively short period, so could skew the simple average. To compare the two, select This period from the view menu and by default it will show both the integrated mean and simple mean temperatures for yesterday when you click Update display. Although average temperatures are not available as webtags, the integrated mean temperature for each day is output to the monthly NOAA style report, and the highest and lowest integrated mean temperature for each month are output to the annual NOAA style report.

Note that statistically, a median temperature could be used, this would require holding all the individual measurements for a day, ranking them in order of magnitude and quoting the central value in that list (again this means extreme values have less skewing effect) - Cumulus does not retain the every minute individual values and cannot calculate median. If you wanted to compare daily median and daily mean, you would need to analyse the monthly log file with an external package.