Thank you,
I search a way to have the average of a colomn not day by day but first day to "current" day for each day (day1 => avg(day1), day2 => avg(day1, day2), day N => avg(day1, ... , dayN).
And then to compare the value of a day with a previous average.
My idea was to save the average and the current date, then to import a previous average througt his date.
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