请教怎么在PPT中用vba实现一个定时器

请问如何在PPT中用vba实现一个定时器?
前提如下:
1.在PPT中有一个excel中的柱状图链接.
2.修改excel的时候实现PPT的实时更新(不用右键点击更新链接来实现).

[解决办法]
参考

VB code

Private Declare Sub Sleep Lib "kernel32.dll" (ByVal dwMilliseconds As Long)Private State As BooleanPrivate Sub Label1_Click()    Dim preT As Date, curT As Long        If State Then        State = False        Exit Sub    End If        State = True    preT = DateAdd("h", 1, Time)        Do        curT = DateDiff("s", Time, preT)        Label1.Caption = Format((curT \ 3600 & ":" & (curT Mod 3600) \ 60 & ":" & (curT Mod 3600) Mod 60), "HH:MM:SS")        DoEvents        Sleep (500)        DoEvents        If Val(curT) < 0 Or Not State Then            Label1.Caption = "stop" '开始考试            Exit Sub        End If    LoopEnd Sub