i have a required where in i need to compare a sales value of selected month with the 12month value of sales
example : if my sales value for july 2017 is 2474
then my ref 12month value of sales should be 26441 (sum of 12month)
my 12 month is a constant from july 2017 to august 2016
help me in writing a calculated field to calculate 12 month value for this in tableau.