The lookup function is a handy calculation you might use to compare today's metrics with previous months years or even custom offset periods. In this video, I show you how it works as we continue to cover functions.
Tableau Notes: https://help.tableau.com/current/pro/desktop/en-us/functions_functions_tablecalculation.htm#lookupexpression-offset
Returns the value of the expression in a target row, specified as a relative offset from the current row. Use FIRST() + n and LAST() - n as part of your offset definition for a target relative to the first/last rows in the partition. If offset is omitted, the row to compare to can be set on the field menu. This function returns NULL if the target row cannot be determined.