I also found this page and it seems to be the best to begin with: http://www.justdata.com.au/Journals/...ll/hull_ma.htm

There I found this formula:

Integer(SquareRoot(Period)) WMA [2 x Integer(Period/2) WMA(Price)
- Period WMA(Price)]

and this is also described in other codes:

MetaStock Formula
period:=Input("Period",1,200,20) ;
sqrtperiod:=Input("Square Root of Period",1,20,4);
Mov(2*(Mov(C,period/2,W))-Mov(C,period,W),sqrtperiod,W);

SuperCharts Formula
Input: period (Default value 20)
waverage(2*waverage(close,period/2)-waverage(close,period), SquareRoot(Period))

I try to work with the first formula and hope that I can make it. First I was confused about the period of the WMA but now I think it must be the squareroot of the period I want to have in the HMA. I keep on testing!

Thanks newdigital!!