Calculate Index% from an expression using ValueList?

[#1]

Hello,

Anyone of you can help me with this please. I have a below expression in a chart which works fine and the Dimensions and Expression show fine without any issues, However

if(ValueList('Pre','Promo','Post','Result')='Pre', num(sum({<TIME_PERIOD_WEEK_NO=p(_WeekPre)>}/ count(_WeekPre)WK_SALES_GROSS_REV),'#,##0'),
if(ValueList('Pre','Promo','Post','Result')='Promo', num(sum({<TIME_PERIOD_WEEK_NO=p(_WeekPromo)>}/count(_WeekPromo) WK_SALES_GROSS_REV),'#,##0'),
if(ValueList('Pre','Promo','Post','Result')='Post', num(sum({<TIME_PERIOD_WEEK_NO=p(_WeekPost)>}/count(_WeekPro) WK_SALES_GROSS_REV),'#,##0'),
num(sum({<TIME_PERIOD_WEEK_NO=p(_WeekPost)>}/Count(_WeekPost) WK_SALES_GROSS_REV) / sum({<TIME_PERIOD_WEEK_NO=p(_WeekPre)>} /Count(_WeekPre) WK_SALES_GROSS_REV) - 1,'#,##0%'))))

in the chart, Now if I want to add another Dimension and column called 'Variance Index %'which is calculated as Post - Pre/ 100 to show in percentage. I was wondering how we can do it, I tried copying the whole expressions for Post and pre and then doing it, also I tried pasting them in variables and using these in the chart, but it doesnt seem to work. Any solution like we use, say if(ValueList(Pre,Post,Promo, Result, Index) = 'Index' 'Pre - Post/100. Please help me with this.

Thanks in Advance