The current WeeWX cumulative series xtype is rather primitive and only produces a series where the first data point is zero and subsequent data points are cumulated by the aggregate interval over the plot time span. The default day, week, month, year plots produced by the image generator cover a (roughly) day, week, month and year from the current time. For example, the day plot starts on a three hour boundary 27 hours before the next three hour boundary after the current time (eg it is 7:30pm as I write this so a default day plot produced now will cover the period from 6:00pm yesterday until 9:00pm tonight). So what? Well if the plot was cumulative the first data point (6:00pm yesterday) would be zero and the plot would cumulate from there. No reset at midnight (or any other time for that matter). Similar effect for week, month and year plots. So a year plot produced today 24 June 2023 would have its first data point on 1 June 2022 (year plots start on the 1st of a month) and it would be zero, the plot then cumulates from that point on until today, 24 June 2023. No reset on 1 January 2023. In other words the value of the last point of the plot will include data from part of last year as well as all of this year.
So the effect your are seeing is expected. Looking at your site the day, week and month plots indeed look correct, not because of the cumulative aggregate behaviour but rather because there was no rain in the plot period before midnight, Sunday and 1 June on the day, week and month plots respectively. If you wait until July you will note you month cumulative plot will be out because it will include rain from June. In time your cumulative day and week plots will show similar 'wrong' data. What to do about it? You either ensure your plots start on the time that you want the cumulative value to reset (eg midnight for day plots) or you change the cumulative series xtype behaviour. Neither can easily be done by the user via config changes. The former is just going to produce ugly plots and will be difficult/messy to implement, modifying the cumulative series xtype has the advantage of needing no change to the WeeWX plot engine. Late last year it got to me and I produced a WeeWX service that replaces the cumulative series xtype shipped with WeeWX with a more capable version that allows the user to specify a reset time for the cumulative value (the service works by placing the more capable cumulative series xtype ahead of the shipped cumulative series xtype in the xtype list so the modified version is always used). I've been using the modified xtype with my solar PV system to report cumulative daily energy since late last year and it seems to work acceptably. I haven't gotten around to implementing it for my (weather) station. If anyone is interested you can find it on GitHub here <https://github.com/gjr80/weewx-xcumulative>. The wiki has some basic details of how to configure the image generator plots to use the reset times as well as some example plots. Note the extension requires WeeWX v4.6.0 or later. Gary -- 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/6021ea4c-2384-496f-ae0e-68986268e6e6n%40googlegroups.com.
