Sub MySub()
Application.Volatile
Dim MyMin As Double
Dim MyMax As Double
MyMin = Worksheets("Sheet1").Cells(1, 1)
MyMax = Worksheets("Sheet1").Cells(1, 2)
ActiveSheet.ChartObjects("Chart 3").Activate
ActiveChart.Axes(xlCategory, xlSecondary).Select
With ActiveChart.Axes(xlCategory, xlSecondary)
.MinimumScale = MyMin
.MaximumScale = MyMax
End With
End Sub