deviation between two lines

[#1]

Hi,

I would like to get the deviation between two lines in a chart.

The calcul would be like a standard deviation calcul ( sum for each dimension value of (line2-line1)^2 )

My problem is that one of my line is calculated with a recursive forumla (the expression uses the above() function).

My chart is would look like this :

- dimension : number

- expression 1 : sum(value)

- expression 2 called  Exp_smooth :

if(number=1,1,
alpha*above(sum(value)) +  (1-alpha)*above(Exp_smooth)
)

I want the standard deviation between to lines

(so I can ajust the alpha parameter in order to minimize the difference between the two expressions)

I don't care if my deviation is in a textbox or an expression in the chart.

You can find an example qvw attached.

THanks for your input !