DAVIS WeatherLink for Windows 4.0 - Manual (Page 104)

T E C H N I C A L R E F E R E N C E
Weather Data Calculations
95
W E A T H E R D A T A C A L C U L A T I O N S
The following section details how the software calculates the data for each
weather function to arrive at an entry for the archive memory or database.
Temperature
The Weatherlink samples the temperature reading from the station a number of
times during the interval and then averages all those readings to arrive at the
average temperature for the interval. The number of times the Weatherlink sam-
ples the temperature depends on the archive interval.
High and Low Temperature
The first time the Weatherlink samples outside temperature during the interval it
writes that value into both a high and low register in memory. Every subsequent
time the Weatherlink samples the temperature, it compares the current value to
the value in the registers and if the current value is higher or lower, replaces the
old value with the current value. Whatever value is in the register at the time of
the archive gets written into archive memory.
Barometric Pressure
The Weatherlink samples the barometric pressure at the time of the archive and
writes that value into the archive memory.
Wind Speed
The Weatherlink samples the wind speed reading the same number of times per
interval as temperature and averages the readings together to arrive at the aver-
age wind speed for the interval.
High Wind Speed
The Weatherlink is constantly checking for a new high wind speed. The highest
wind speed value recorded during the interval gets written into archive memory.
Wind Direction
The Weatherlink samples the wind direction reading the same number of times
per interval as temperature. If wind speed is greater than 0 when the Weatherlink
samples wind direction, it places a “marker” into one of sixteen “bins” which cor-
respond to the sixteen compass points. At the time of the archive, the Weatherlink
A RCHIVE I NTERVAL S AMPLE R ATE
1 minute every 5 seconds
5 minutes every 5 seconds
10 minutes every 5 seconds
15 minutes every 8 seconds
30 minutes every 15 seconds
1 hour every 30 seconds
2 hours every 60 seconds