Thanks!  You mind pointing me at a reference implementation of a service 
class that does this all correctly?  I'm likely able to get it working on 
my own if I see how it is to be done.

On Friday, December 17, 2021 at 2:11:13 AM UTC-8 gjr80 wrote:

> Any values have to be analysed in context of the unit system of the packet 
> into which they are inserted. The unit system of packets emitted by the sdr 
> driver when reading acurite devices is either US customary or metric 
> depending on the sensors being read. As far as I can tell the purple air 
> extension you are using does not perform any check of the unit system of 
> the loop packet (loop packet field usUnits) to which pressure is added, but 
> I could be wrong. Normally you would find something in the method of the 
> service class that is bound to the NEW_LOOP_PACKET event (in this case 
> Purple.new_loop_packet()) that checks usUnits and converts pressures, 
> temperature, speeds etc to match the packet units. Or if not in that method 
> in the code called by that method. 
>
> I’m not about to try to debug someone else’s extension, especially one as 
> complex as this. John, the author, frequents the forums so give it a day or 
> so and see if he comments. Otherwise I suggest you raise an issue in his 
> repo.
>
> Gary
>
> On Friday, 17 December 2021 at 19:16:38 UTC+10 [email protected] wrote:
>
>> Well,  I have basically two sources: acurite sensors via sdr and the 
>> purple api via a purple api plugin.  The acurite sensors don't expose 
>> pressure and the rtl433 logs never indicate that a pressure is detected in 
>> the acurite information.  
>>
>> The purple api does expose pressure and it comes in as millibars: 
>> 200 success { "api_version" : "V1.0.10-0.0.12", "time_stamp" : 1639725648
>> , "data_time_stamp" : 1639725596, "sensor" : { "sensor_index" : 81961, 
>> "pressure" : 1018.5 } }
>>
>> That said there are log lines that indicate the pressure was read from 
>> purple and included as inHg in the result.
>>
>> weewx[1] DEBUG user.purple: Inserted packet[pressure]: 30.096963 into 
>> packet.
>>
>> I've run the purple plugin locally and verified that is is converted to 
>> inHg.  The conversion happens here: 
>> https://github.com/chaunceygardiner/weewx-purple/blob/e7f214539b63281d74af9e90810045dd8d1b7b80/bin/user/purple.py#L266.
>>   
>> Is this the proper way of doing it?  If not, can you point me to an example 
>> of doing it properly in a plugin?
>>
>>
>>
>>
>>
>> On Friday, December 17, 2021 at 12:39:29 AM UTC-8 gjr80 wrote:
>>
>>> What driver are you using and what is the source of the pressure value? 
>>> This sounds very much like a service is being used to add one or more of 
>>> the three pressure fields (altimeter, barometer or pressure) to 
>>> packets/records from the driver and the unit system of the packet/record is 
>>> not being checked and followed. This can result in fields being added to 
>>> packets/records in the wrong units which eventually results in a double 
>>> unit conversion.
>>>
>>> The answer will almost certainly be related to the source of one of the 
>>> three pressure fields.
>>>
>>> Gary
>>> On Friday, 17 December 2021 at 17:56:10 UTC+10 [email protected] wrote:
>>>
>>>> BTW, running on Develop
>>>>
>>>> On Thursday, December 16, 2021 at 11:54:46 PM UTC-8 Joel Baranick wrote:
>>>>
>>>>> What is the best way to determine the source of a metric which fails 
>>>>> QC?  The failure in this case is the "pressure" metrics which is expected 
>>>>> to be in inHq.  The QC error is: `LOOP value 'pressure' 
>>>>> 0.8885885448234093 
>>>>> outside limits (24.0, 34.5)`.  It seems like the pressure is converted to 
>>>>> inHq correctly: `Inserted packet[pressure]: 30.091057 into packet.`. But, 
>>>>> it seems like the  30.091057 is being be fed back into the conversion 
>>>>> function.
>>>>
>>>>

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