Hi guys

i have this urgent task to do which i have no idea how to do , i have tried different ways but it doesn't seem to work

i have the report below

i need to show get the difference between  level 1 and 2  results and over all scores by month in a different column

so it should look like the example below ( roughly done on excel)

so on my tableau report i need a diff column showing the difference like the example above.

Can this be done?

if any one can help i will be very great-full