Hello,

I'm quite new to Tableau and I've read up all I could find on trend lines and dates but I see a quite interesting behavior and I cannot find a solution.

I cannot share the data, but the specifics are:

Initial session date - DATE&TIME  dimension

Distinct UserID - Calculated field: COUNTD(User_ID) where USER_ID is string - used for simplicity

I'm plotting Distinct UserID against DAY(Intial session date) as seen in the below screenshot. I can plot trend lines with this but the issue is that since DAY(Initial session date) is a DAY_PART it aggregates across all same days of months etc. and I need distinct days.

Now when I change to DAY_VALUES trend lines break and its not able to calculate any more. Standard error comes up which I don't really get.

...and as another strange behavior if I change  DAY(Intial session date) to discrete I can still have the trend lines IF DAY is DAY_PART.

All help is appreciated as this way the calculation and trend is not the correct one.

Cheers