Unless I'm reading it wrong, it would be a table calculation written in the same way you would mathematically or in excel.

You could try using offset to offset by 3 months.

There's probably a better option but what I would do is..Table calculation for mean,Table calculation using mean to find upper and another to find lower... mean +/- stddev_pop({measure}).This will give you 3 lines and perhaps it's possible to use are...

Have you tried something like this?sum(offset_list(${measure},0,12))offset list starts at 0 for same line, so if you want to include the current month or 1 if you want to go back 1 month. Then it will sum the last 12 from there.You may need to play w...

Not sure it will work but you could add a field with just a numeric value and try using & adjusting that to size the points.