How to get value in previous column and another row from Matrix with Custom Code?

Question

I want to calculate the value of tb_Open and tb_Close. I try to use custom code for calculate them. tb_close is correct but tb_Open is not correct that show value = 0 .
This is example report:
* I have 2 Dataset , Dataset1 is all data for show in my report. Dataset2 is only first Open for first month
* First value of Open is item field in Dataset2 and this value only for first month (january). But for other month Open value get from Close in previous month.
Detail for Red number:
1. tb_Open -> tb_Close in previous month but first month from item field in Dataset2
expression =FormatNumber(Code.GetOpening(Fields!month.Value,First(Fields!open.Value, "Dataset2")))
2. tb_TOTAL1 group on item_part = 1
expression =FormatNumber(Sum(CDbl(Fields!budget.Value)))
3. tb_TOTAL2 group on item_part = 3 or item_part = 4
expression =FormatNumber(Sum(CDbl(Fields!budget.Value)) + ReportItems!tb_TOTAL1.Value )
4. tb_TOTAL3 group on item_part = 2
expression =FormatNumber(Sum(CDbl(Fields!budget.Value)) - ReportItems!tb_TOTAL2 .Value)
5. tb_Close -> calculate from tb_TOTAL3 - tb_Open
expression =FormatNumber(Code.GetClosing(ReportItems!tb_TOTAL3.Value,ReportItems!tb_Open.Value))
My custom code:
Dim Shared prev_close As Double
Dim Shared now_close As Double
Dim Shared now_open As Double
Public Function GetClosing(TOTAL3 as Double,NowOpening as Double)
    now_close = TOTAL3 + NowOpening
    prev_close = now_close
    Return now_close
End Function
Public Function GetOpening(Month as String,NowOpen as Double)
    If Month = "1" Then
        now_open = NowOpen
    Else    
        now_open = prev_close
    End If
    Return now_open
End Function
Thanks alot for your help!
Regards
Panda A

Answer 1

Looks okay to me.
Perhaps the variables should be declared as public (?)