I'm not sure what is confusing here. $span(hour_delta=720).length gives us
a ValueHelper whose included ValueTuple covers a span of 720 * 3600
seconds. If the 720 hour period covers a DST start time the actual span
will be 719 * 3600 seconds due to WeeWX being DST unaware. The .day
converts the number of seconds to decimal days, assuming a DST start time
is included the result is 29.958333 days (29 + 23/24ths). The .format("%d")
simply formats this number as an integer giving the expected 29.
The .long_form applies slightly different formatting. Again assuming the
hour_delta=720 covers a DST start time, and due to WeeWX DST naivety, the
$span(hour_delta=720).length gives us a ValueHelper whose included
ValueTuple covers a span of 719 * 3600 seconds. .long_form formats a span
in seconds using a longer, human friendly format; if using the defaults an
'hours, minutes, seconds' format will be used. Since we have exactly 719
hours in the span the result is '719 hours, 0 minutes, 0 seconds'.
There are no rounding errors as such, just two different tags applying
slightly different formatting. Perhaps there is something else that is
confusing that I am not seeing.
Gary
On Friday, 25 April 2025 at 19:21:49 UTC+12 [email protected] wrote:
> Playing a little around, this is confusing me:
> $span(hour_delta=720).length.day.format("%d")
> => 29 days. Okay...
>
> $span(hour_delta=720).length.long_form
> => 719 hours, 0 minutes, 0 seconds. ???
> So, for the hours, I can't think of a scenario, where I consider this as a
> correct result, and there isn't room for a rounding issue.
>
> Nailing it down to the DST change, with the following lines
> $span(hour_delta=632).length.long_form
> $span(hour_delta=631).length.long_form
> $span(hour_delta=630).length.long_form
> $span(hour_delta=629).length.long_form
> I get these results:
> 631 hours, 0 minutes, 0 seconds
> 630 hours, 0 minutes, 0 seconds
> 630 hours, 0 minutes, 0 seconds
> 629 hours, 0 minutes, 0 seconds
>
>
> Karen K schrieb am Donnerstag, 24. April 2025 um 21:07:02 UTC+2:
>
>> [email protected] schrieb am Donnerstag, 24. April 2025 um 11:41:39
>> UTC+2:
>>
>> But anyway, I also wonder what is really the issue. It may or may not be
>> just the label. depending on how the day_delta sum is calculated. Is it the
>> sum of the archive_day sums? Is it the sum of archive's rain column, over
>> 30 x 24h?
>>
>>
>>
>> May be, it is a matter of rounding. If the time period is 29 days and 23
>> hours, it is almost 30 days, but if you omit rounding it is 29 days.
>>
>> Internally all timestamps are seconds since 1970-01-01 00:00:00 UTC. To
>> get a timespan of days WeeWX uses the functions
>> weeutil.archive{Day,Week,Month,Year}Span(), which convert the value
>> into a tuple of year, month, day, hour, minute, second local time, sets
>> hour, minute, second to 0, applies the appropriate amount of days, and
>> finally converts both ends back to seconds since 1970-01-01 00:00:00 UTC.
>> If the timespan includes a daylight saving time switch, it is - in seconds
>> - not whole days but an hour more or less.
>>
>>
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