Be careful here, for most observations the default avg extractor function 
is appropriate (that's why it is the default) as the extracted value is a 
representation of the observation over the entire archive period. The 
majority of observations handled by a default WeeWX install (ie outTemp, 
barometer, radiation etc) use the avg extractor function. The last extractor 
function is typically used for extensive observations such as day rainfall 
or perhaps a sensor state observation such as signal level that is either 0 
or 1 where the latest value is of interest.

Ultimately though it is personal choice. 

Gary
On Tuesday 9 January 2024 at 06:30:23 UTC+10 [email protected] wrote:

> 1. There are defaults and you only have to configure any settings that you 
> want to be different. So in your example you would only have to override 
> the extractor.
> [Accumulator]
>      ...
>      [[XField]]
>          extractor = last
>
> 2. I don’t know the answer, but they have a different meaning. See, 
> http://www.weewx.com/docs/4.10/devnotes.htm#value_None.
>
> If you are adding new observations be sure to read up on units and 
> unit_groups, 
> http://www.weewx.com/docs/4.10/customizing.htm#customizing_units.
>
> On Sunday 7 January 2024 at 04:34:28 UTC-5 Remy Lavabre wrote:
>
>> Thank you for the answer ! Perfect...
>>
>> Only two questions still bothers me:
>>
>> - 1/ I added an “XField” field to my weewx.sdb database. This XField 
>> corresponds to a simple parameter such as temperature or pressure. It is 
>> incorporated into the "PacketsLoop".
>>
>> Do we absolutely have to declare [Accumulator] in weewx.sdb as follows:
>>
>>
>>
>>
>>
>>
>>
>> *[Accumulator]     ...     [[XField]]         accumulator = scalar        
>>  adder = add         merger = minmax         extractor = last*
>>
>> or are there default parameters in weewx in a (new) field of unknown type 
>> in a database?
>>
>>
>> - 2/ Concerning "PacketsLoop": the weewx documentation stipulates that 
>> they can be complete (all fields in the database) or partial.
>>
>> But are the two PacketsLoops below interpreted in the same way?
>>
>> data1 = {'dateTime': mydatetime, 'usUnits': 'METRIC', 'outTemp': '31',* 
>> 'outHumidity': None*, 'dewpoint': '28'}
>> data2 = {'dateTime': mydatetime, 'usUnits': 'METRIC', 'outTemp': '31',  
>> 'dewpoint': '28'}
>>
>> Thank you for your help - Kind regards
>>
>> Le samedi 6 janvier 2024 à 22:34:41 UTC+1, [email protected] a écrit :
>>
>>> check out, https://github.com/weewx/weewx/wiki/Accumulators
>>>
>>> On Saturday 6 January 2024 at 10:27:48 UTC-5 Remy Lavabre wrote:
>>>
>>>> Good morning,
>>>>
>>>> Wishing to write a driver for WeeWX in order to automatically retrieve 
>>>> and integrate AWEKAS data into the weewx.sbd database, I have a question 
>>>> regarding the management of "PacketsLoop" data:
>>>>
>>>> The Weewx documentation states that for temperatures, it is an average 
>>>> of the "packetsloop" received during the time period set in weewx.conf 
>>>> (300 
>>>> seconds for example), that for rain it is the maximum of packetsloop. -> OK
>>>>
>>>> But for the other data? What about it?
>>>>
>>>> If we add personal fields to the database, such as electricity 
>>>> consumption. What will be the value of this field in the database -> An 
>>>> average of packets received, the maximum value, the last?
>>>>
>>>> And is it possible to specify to wewx (and if so where and how...), 
>>>> what type of result we want to have with the aggregation of a field from 
>>>> several loop packets?
>>>>
>>>> thank you
>>>>
>>>

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