Private Sub Workbook_Open()
    Dim maxWidth As Integer
    Dim maxHeight As Integer
    Application.WindowState = xlMaximized
    maxWidth = Application.Width
    maxHeight = Application.Height
    Call CenterApp(maxWidth, maxHeight)
End Sub

Sub CenterApp(maxWidth As Integer, maxHeight As Integer)
    Dim appLeft As Integer
    Dim appTop As Integer
    Dim appWidth As Integer
    Dim appHeight As Integer
    Application.WindowState = xlNormal
    appLeft = maxWidth / 2
    appTop = maxHeight / 2
    appWidth = maxWidth / 16
    appHeight = maxHeight / 30
    Application.Left = appLeft
    Application.Top = appTop
    Application.Width = appWidth
    Application.Height = appHeight
End Sub