+ While it is the best way to define calculated values by writing a search list extension or XTYPE extension, + sometimes it is easier or faster to include the calculation in the template. To do so, Cheetah provides + the #set directive. Here it is explained how to use it for calculations and + displaying the resulting values. +
++ To get an observation type value in a way that can be used in formulae you can add .raw + after an observation type tag. +
++ Example: +
+$almanac.sun.rise.raw+
+ To calculate - for example - the daylight time: +
+#set $daylight=$almanac.sun.set.raw-$almanac.sun.rise.raw+
+ To display that value and make it observe the units and settings is a little bit tricky: +
+#from weewx.units import ValueTuple,ValueHelper +#set $rising=$almanac.sun.rise.raw +#set $setting=$almanac.sun.set.raw +#set $daylight=$setting-$rising +#set $daylight_vh=ValueHelper(ValueTuple($daylight,'second','group_deltatime'),formatter=$station.formatter) + +$daylight_vh+
The unit provided has to conform to the unit of the raw values used in calculation.
+To get a special output format you can add .format(...), for example:
+$daylight_vh.format("%(hour)d%(hour_label) %(minute)d%(minute_label)s %(second)d%(second_label)s","")
+
+ + Another example is the difference between maximum and minimum temperature of the day in Kelvin + (which is the same value as in degrees Centigrade for differences, so no unit conversion applies): +
+#from weewx.units import ValueTuple,ValueHelper +#set $maxmin=$day.outTemp.max.degree_C.raw-$day.outTemp.min.degree_C.raw +#set $maxmin_vh=ValueHelper(ValueTuple($maxmin,'degree_C','group_temperature'),formatter=$station.formatter) + +$maxmin_vh.format(add_label=False) Kelvin+