Kiran, many thanks for the prompt reply.
I have used your syntax and found that I must select both years to obtain the previous years data at the same time as the year I want to see data for.
Therefore if I wanted to see the primary data for 2016 and just wanted to see secondary data for 2015 I must select both 2015 and 16.
I think something went wrong the expressions I have given you are for eg, in real with out selections the first expression gives the sales for the Max year and second one gives for previous year.
Load * Inline [
Now try my expression in a text objects