Option Explicit
Public dTime As Date

Sub ValueStore()
Dim NR As Long
NR = Range("I" & Cells(Rows.Count).Row).End(xlUp).Row + 1
Range("I" & NR).Value = Range("A1").Value
If NR > 30 Then
  Range("I2").Delete xlShiftUp
  Sheets("Blad1").ChartObjects("Diagram 4").Chart.FullSeriesCollection(1).Values = "=Blad1!$I$2:$I$30"
End If
Call StartTimer
 End Sub


 Sub StartTimer()
dTime = Now + TimeValue("01:00:00")
Application.OnTime dTime, "ValueStore", Schedule:=True
End Sub


Sub StopTimer()
 On Error Resume Next
Application.OnTime dTime, "ValueStore", Schedule:=False
End Sub