Many Thanks Tom that clears it up. Mike On Wednesday, October 21, 2020 at 12:56:28 PM UTC+1 [email protected] wrote:
> A bit of background. WeeWX manages two different sets of databases. > > First is the main archive table. It is updated with every archive record. > > Then there is a set of "daily summaries." These contain the minimum, > maximum, time of minimum and maximum, and some other details for each > observation type for each day. It is updated with every LOOP packet, so > despite having only one record per day, it can be quite precise about when > minimums and maximums happen. Lookups using daily summaries can also be > much faster, but they require that the aggregation period run precisely > midnight-to-midnight. > > On to the problem. When WeeWX evaluates a tag such as $day.outTemp.min, > you are asking for the minimum since midnight, so the daily summaries are > used. This gives an answer down to the resolution of the LOOP packets. > > But, for a tag like $span($hour_delta=24), the aggregation period does > not run midnight-to-midnight, so the archive table must be used. So, the > results have a resolution no better than the archive period. > > With your dataset, the minimum of 984.9 happened at 10:38:36 and the daily > summaries captured it. But if you were to look in your archive table, it > would show 985.0 at 10:20:00, because that's the average over the 5 minute > archive period. > > If you hate this result, you can tell WeeWX not to use the LOOP packets to > update the daily highs and lows by setting option loop_hilo under > [StdArchive] to False. This will cause the daily summaries to be updated > with the min and max archive records, rather than LOOP packets. > > Hope this helps. > > -tk > > On Wed, Oct 21, 2020 at 3:37 AM Mike Thompson < > [email protected]> wrote: > >> Hi All, >> >> I'd like to have information over the last 24 hours and I thought I could >> easily achieve this by defining a $span tag but it's not worked out as I >> thought. >> >> I've defined the tag as $span($hour_delta=24) and as $span($day_delta=1) >> both give the same results. >> >> To test I changed the Seasons statstics.inc to include my 24hrs as >> follows; >> >> #set $archive_data = [$day,$yesterday,$span($hour_delta=24), >> $week,$seven_day, $month, $year, $alltime] >> >> This seems to work ok as shown below >> >> >> >> >> But there is the occasional anomaly for example looking at the min >> Barometer it shows; >> 984.9 for today @ 10:38:36 >> 988.1 for yesterday @ 09:54.36 and >> 985.0 for last 24 hours @ 10:20 >> >> I was expecting the min for last 24 hrs to be equal to or less than >> today's value (984.9 is less than 985) but it's not, why is that? >> >> It doesn't just happen with min barometer it is the same with max temp >> which was yesterday's example. >> >> Appreciate your thoughts >> Thanks in Advance >> Mike >> >> extract from Seasons statistics.inc showing min Barometer >> <tr> >> <td class="label">$obs.label.barometer</td> >> <td class="units">$unit.label.barometer</td> >> #for $archive in $archive_data >> <td class="data >> new_row">$archive.barometer.max.format(add_label=False)<br/> >> <span class="timestamp">$archive.barometer.maxtime</span><br/> >> $archive.barometer.min.format(add_label=False)<br/> >> <span class="timestamp">$archive.barometer.mintime</span> >> </td> >> #end for >> >> -- >> You received this message because you are subscribed to the Google Groups >> "weewx-user" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/weewx-user/69f8d05a-f536-4be2-9b89-468684983cf5o%40googlegroups.com >> >> <https://groups.google.com/d/msgid/weewx-user/69f8d05a-f536-4be2-9b89-468684983cf5o%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- You received this message because you are subscribed to the Google Groups "weewx-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-user/23f02b12-c405-49db-8a93-8dc8c656948cn%40googlegroups.com.
