Scatter Plot reference lines

[TomBond77]

Hi experts

I am referring to this solution: https://community.qlik.com/t5/New-to-QlikView/Dynamically-position-the-reference-line-on-a-scatter-p... 

I tried to adapt this logic, but getting the message "Error in expression, Aggr. takes at least two parameters"

=Max(Aggr(Sum({<[Reporting Time]={'YTD'}>} [Revenue]) + Sum({<[Reporting Time]={'YTD'}>} [Cost])),[Cost Center]))/2

any ideas how to solve this issue?

Kind Regards

Tom