I have two lists both with two columns as follows

List one
Customers Turnover 2013-2014

List two
Customer Turnover 2014 -2015

What I want to do is compare the turnover of 2013/2014 to the turnover with 2014 -2015

There are differences between the lists in that new customers will be added across the year so the customers on list two will grow and will differ in that respect from list one

How can I do approach this