This will close the Calculator.
Code:
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function PostMessage Lib "user32" Alias "PostMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Const WM_CLOSE = &H10
Const WM_DESTROY = &H2
Private Sub Command1_Click()
'Find the hWnd of the Calculator
hParent = FindWindow("SciCalc", "Calculator")
'FindWindow(Class, Caption)
'If found then...
If hParent <> 0 Then 'close it
PostMessage hParent, WM_CLOSE, 0, 0
PostMessage hParent, WM_DESTROY, 0, 0
End If
'Closed
End Sub