The Weatherlink samples the humidity only once at the time of the archive and writes that value into the archive memory.
The dew point is not stored in archive memory, rather it is calculated as the data gets written to the database file. The software calculates dew point based on the temperature for the archive period (that is, the average temperature during the interval) and an approximation of the average humidity during the interval.
To arrive at an "average" outside humidity reading, the software averages the outside humidity for the current archive interval and the previous archive interval (if available). If no earlier entry exists in the archive memory, the Weatherlink calculates dew point based on the current outside humidity and the average temperature.
These descriptions were taken from the "ReadMe" file included with the Davis Instruments, Weather Link software package. The descriptions have been modified to suit the specifics of our implementation.
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