Check line 370, file wxservices.py
<https://github.com/weewx/weewx/blob/master/bin/weewx/wxservices.py#L370>

-tk

On Thu, May 3, 2018 at 9:59 AM, John Hill <[email protected]> wrote:

> Hi Thomas,
> Sorry to rehash an old thread, but I was looking though your wxformulas.py
> for more info on the ET calc.  As you mentioned, ET used to be calculated
> as a rate but now is just a measured quantity, like rain.  However, the
> calcs and the examples in wxformulas.py still reference a rate.
>
> For example, line 687:
> Returns: Evapotranspiration in mm/hr
> Example (Example 19 in the reference document):
> >>> sr_mean_wpm2 = 680.56 # == 2.45 MJ/m^2/hr
> >>> timestamp = 1475337600 # 1-Oct-2016 at 16:00UTC
> >>> print "ET0 = %.2f mm/hr" % evapotranspiration_Metric(Tmin_C=38,
> Tmax_C=38, rh_min=52, rh_max=52,
> ... sr_mean_wpm2=sr_mean_wpm2, ws_mps=3.3, wind_height_m=2,
> ... latitude_deg=16.217, longitude_deg=-16.25, altitude_m=8,
> timestamp=timestamp)
> ET0 = 0.63 mm/hr
> Another example, this time for night
> >>> sr_mean_wpm2 = 0.0 # night time
> >>> timestamp = 1475294400 # 1-Oct-2016 at 04:00UTC (0300 local)
> >>> print "ET0 = %.2f mm/hr" % evapotranspiration_Metric(Tmin_C=28,
> Tmax_C=28, rh_min=90, rh_max=90,
> ... sr_mean_wpm2=sr_mean_wpm2, ws_mps=3.3, wind_height_m=2,
> ... latitude_deg=16.217, longitude_deg=-16.25, altitude_m=8,
> timestamp=timestamp)
> ET0 = 0.03 mm/hr
>
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