Index comparison unaffected by selections

[Hoowling]

Hi community, 

I would like to compare historical stock prices to an index. 
All stocks and indexes are located in the same dimension: Bolagsdata.Bolagsnamn. 
The price data is stored in another dimension: Closeprice. 

In below graph the expression is simply "=Closeprice" , over a period dimension. 
I want to display the index in the graph, which is "OMXS ALL GI" (see below list box), regardless of which stock that is selected. 

Any thoughts on how to achieve this? 

[dplr-rn · Accepted solution]

try something like below. basically first part shows all possible values of product and second part forces 1 product to be always shown

Sum({
<Product=p(Product)>
+<Product={'All-Purpose Bike Stand'}>}
Sales)

[Hoowling]

Thanks! The correct expression to use was the second part of your suggested expression: 

Sum({
<Bolagsdata.Bolagsnamn={'OMXS ALL GI'}>}Closeprice)