Average and STDV using above diagramm function

[BHoll]

Hello everyone,

i'm trying to create a line diagramm where the graph show the difference betweend a value  Point and the value Point before (see attachment)

Therefore im using the formula  Value - above(Value).

Now i want to add 3 more graphs/lines . The Average of  Value - above(Value)  and the Average + 2* Stdv(Value - above(Value)) and Average of Value - above(Value)  - 2* Stdv(Value - above(Value)).

My initital thought was to use a formula like this to get the average: 

sum(Total(Value - above(Value) ) / (Count(Value) - 1)

But it seems that QlikView is not able to use Aggregation functions together with the above() formula.

Any ideas how to solve my Problem?

best regards,

BHoll