how to execute this code - Argument not optional

I have the following code that shows how to print from a flexgrid in VB6.   The only problem is that I don't know how to call this routine in my command button on my form.  

I get the error "argument not optional."  Can someone explain why that happens

Private Sub Command4_Click()
Call PrintFlexGrid
End Sub

Private Sub PrintFlexGrid(ByVal ptr As Object, ByVal flx As _
    MSFlexGrid, ByVal xmin As Single, ByVal ymin As Single)
Const GAP = 60

Dim xmax As Single
Dim ymax As Single
Dim X As Single
Dim c As Integer
Dim r As Integer

    With ptr.Font
        .Name = flxData.Font.Name
        .Size = flxData.Font.Size
    End With

    With flxData
        ' See how wide the whole thing is.
        xmax = xmin + GAP
        For c = 0 To .Cols - 1
            xmax = xmax + .ColWidth(c) + 2 * GAP
        Next c

        ' Print each row.
        ptr.CurrentY = ymin
        For r = 0 To .Rows - 1
            ' Draw a line above this row.
            If r > 0 Then ptr.Line (xmin, _
                ptr.CurrentY)-(xmax, ptr.CurrentY)
            ptr.CurrentY = ptr.CurrentY + GAP

            ' Print the entries on this row.
            X = xmin + GAP
            For c = 0 To .Cols - 1
                ptr.CurrentX = X
                ptr.Print BoundedText(ptr, .TextMatrix(r, _
                    c), .ColWidth(c));
                X = X + .ColWidth(c) + 2 * GAP
            Next c
            ptr.CurrentY = ptr.CurrentY + GAP

            ' Move to the next line.
            ptr.Print
        Next r
        ymax = ptr.CurrentY

        ' Draw a box around everything.
        ptr.Line (xmin, ymin)-(xmax, ymax), , B

        ' Draw lines between the columns.
        X = xmin
        For c = 0 To .Cols - 2
            X = X + .ColWidth(c) + 2 * GAP
            ptr.Line (X, ymin)-(X, ymax)
        Next c
    End With
End Sub

' Truncate the string so it fits within the width.
Private Function BoundedText(ByVal ptr As Object, ByVal txt _
    As String, ByVal max_wid As Single) As String
    Do While ptr.TextWidth(txt) > max_wid
        txt = Left$(txt, Len(txt) - 1)
    Loop
    BoundedText = txt
End Function

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