Attached is a simple plot of mine showing a timeseries, with reference lines for the historical average and the historical stddev ("-1,1 standard deviation").
What confuses me though is that the stdev band is about half what I would expect it to be. The width of the band is: 3.934 - 3.416 = 0.518. But as you can see by the graph on the bottom the stddev NEVER goes below 0.6 (in fact, the stddev is 0.940 over 422 data points).
Does anyone understand how tableau is doing this calculation?
Would need to see the workbook to been sure, but my guess is that you are plotfing daily (?) averages so the reference line is nust zhowing the std of the daily averages. Reference, each lines are calculated on the aggregate values retjrned to Tableau.