As part of my experimenting with the EasyWeather software that came with my weather station I’ve managed to decipher the meaning of most of the numbers in the EasyWeather.dat file. It’s a plain text file, with comma separated values (i.e. CSV format). The table below shows what I think each column means.
After a few months I stopped using EasyWeather, as I’d developed my own alternative software to run on a low power embedded Linux box. For more details about this software, and links to other weather station software, see my main weather station page.
| Column | Item | Format | Comments |
|---|---|---|---|
| 1 | record number | integer | starts at 1 |
| 2 | transfer date | yyyy-mm-dd hh:mm:ss | date and time (according to computer, not weather station) of transfer from station to file |
| 3 | reading date | yyyy-mm-dd hh:mm:ss | date and time of record. Appears to be derived from computer’s clock at time of transfer |
| 4 | reading interval | integer | minutes since previous reading |
| 5 | indoor humidity | integer | relative humidity percent |
| 6 | indoor temperature | floating point | degrees centigrade |
| 7 | outdoor humidity | integer | relative humidity percent |
| 8 | outdoor temperature | floating point | degrees centigrade |
| 9 | dew point | floating point | degrees centigrade. See comments below |
| 10 | wind chill | floating point | degrees centigrade. See comments below |
| 11 | absolute pressure | floating point | millibars |
| 12 | relative pressure | floating point | millibars |
| 13 | wind average | floating point | metres / second |
| 14 | wind average | integer | Beaufort |
| 15 | wind gust | floating point | metres / second |
| 16 | wind gust | integer | Beaufort |
| 17 | wind direction | integer | 0 to 15. 0 is north, 1 is NNE, 8 is south, 15 is NNW |
| 18 | wind direction | text | ENE appears as NEE, ESE appears as SEE |
| 19 | rain ‘ticks’ | integer | cumulative count of number of times rain gauge has tipped. Resets to zero if station’s batteries removed |
| 20 | rain total | floating point | mm rain total. Column 19 * 0.3, but does not reset to zero, stays fixed until ticks catch up |
| 21 | rain since last reading | floating point | mm |
| 22 | rain in last hour | floating point | mm |
| 23 | rain in last 24 hours | floating point | mm |
| 24 | rain in last 7 days | floating point | mm |
| 25 | rain in last 30 days | floating point | mm |
| 26 | rain total or in last year? | floating point | mm. This is the same as column 20 in my data |
| 27 | status bit 0 | integer | 0 or 1 |
| 28 | status bit 1 | integer | 0 or 1 |
| 29 | status bit 2 | integer | 0 or 1 |
| 30 | status bit 3 | integer | 0 or 1 |
| 31 | status bit 4 | integer | 0 or 1 |
| 32 | status bit 5 | integer | 0 or 1 |
| 33 | status bit 6 – outdoor readings invalid | integer | 0 or 1 |
| 34 | status bit 7 | integer | 0 or 1 |
| 35 | data address | 6-digit hexadecimal | pointer to where in weather station’s memory data came from. Range is 000100 to 00FFF0. After reaching 00FFF0, returns to 000100 – i.e. a circular or ring buffer. |
| 36 | raw data | 16 2-digit hexadecimals | the raw data as it came from the weather station |
The dew point and wind chill values are computed from outdoor temperature, outdoor humidity and average wind speed. I have found formulae on various web sites, but none exactly matches the values in the data file.
Dew point is computed as follows:
a = 17.27
b = 237.7
gamma = (a * t / (b + t)) + ln(rh / 100.0)
dew = b * gamma / (a - gamma)
Wind chill is a bit more complicated. There are various quite different formulae, with some variation by country. The best bet I’ve found so far is this:
wc = 13.12 + (0.6215 * t) - (11.37 * (v**0.16)) + (0.3965 * t * (v**0.16))
Since writing the above Phil Maddocks has sent me a much better formula, based on Court’s formula for Heat Loss:
if t < 33 and v >= 1.79:
wc = 33 + ((t - 33) * (0.55 + (0.417 * sqr(v)) - (0.0454 * v)))
else:
wc = t