Excel user defined function to easily set the RTD throttle. http://msdn.microsoft.com/en-us/library/office/aa140060(v=office.10).aspx#odc_xlrtdfaq_howconfigrtdthrottle

Excel-SetRTDUpdaterate

Public Function SetRTDUpdateRate(mSeconds As Long) As String
    'Set RTDUpdate Rate registry value
    Application.RTD.ThrottleInterval = mSeconds
    SetRTDUpdateRate = mSeconds & " mS"
End Function