Reference line in chart

[#1]

Hello All,

I am looking to have a reference line in my chart which would give previous years Ontime %average based on year selection. i.e if 2009 selected than 2008 average is given.

Ontime % is calculated per distinct Document Numbers received based on receive date selection.

I am able to show average as per the same year selection by the expression

=-sum(aggr([Transit Time] >= ([Receipt Date] - [Ship Date]),[Doc. Number]))/count(distinct [Doc. Number]

How Can i include previous year parametr within this expression.

Thansk for any help.

Kiran.

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