% [ColumnA] vs [ColumnB] using THEN sum([Value]) OVER (AllPrevious([Axis.X]))
Presently I have KPI Chart 'Comparative Value' expression as shown

Sum([Net TY]) THEN sum([Value]) OVER (AllPrevious([Axis.X]))
[Net TY] is the column containing Net Sales This Year. I have another column [Net LY] showing the previous year's sales.
I'd like to replace the above expression to show the % Variance between TY and LY sales. Normally this is easy: sum([Net TY] )/ sum([Net LY])1
The question is, how do I make this work in the above OVER expression?
TIA...
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