create a chronometer on excel

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In the mTimer3 module :

Private Sub Chrono()
Dim T As Double
    T = TimeValue(UserForm3.LblTemps.Caption) - TimeSerial(0, 0, 1)
    UserForm3.LblTemps.Caption = Format(T, "hh:mm:ss")
    If T = 0 Then TimerOff

'///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
'As an alternative you could try making a call to a separate Sub with the sound command/s, instead of placing the code here.   
 
    If UserForm3.LblTemps.Caption = "00:59:55" Then '<--- set the time for sound here
        Beep  '<-- place your command here for sound
    End If
'\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

End Sub