How to Calculate Previous Year Sales in Tableau Using a Lookup Function

How do you calculate the previous year sales in tableau example I have a view showing some of sales by each year let's add a calculated field call it previous year we're going to type a lookup function we're going to look up sum of sales comma negative one that's going to give the previous year's sales click apply okay and drag previous year into the view to give us measure names and measure values and you can see for each year it brings in the previous value .