Calculating confidence intervals for rolling 28 day period?

Hi. I'm really struggling with window functions in Tableau. For this case, I need to calculate the standard deviation of all data points in the past 28 days. The problem is I am displaying this with a date in the x axis, and Tableau only wants to do windows functions on the level in view. For example, window_avg with dates in view will give you the average daily average (or sum or whatever) but not the true average of all data points in the previous 28 days. For average you can get around this with window sum / window count, but with stdev i have not found a solution. Please help if you can. Regards

Also, I need to pass 28 day sets of data to python to use the T inverse function for this and I haven't found a way to pass all rows (dis aggregated) from a window 😭