Get dimension value in expression

[#1]

Is there any way to get dimension value inside expression using set anaysis?

I need to get average sum of previous values not using function above.

Amount of "steps" for average sum calculations is set by slider value.

Also, if I select some values if field "Num" it should calculates correctly.

There is only one problem, it calculates correctly only for the maximum value in field "Num".

For all previous values resulting value is incorrect.

Please advice how to correct formula to let it calculate correctly fot all other "Num" values?

It works now only for one max value...

There is .qvw file with all calculations and formulas.

Please see some screenshots of chart with correct/incorrect values.

Thanks in advance!