CCacheEntry<T>::ContainsValue

// CoAcme4321.cpp
STDMETHODIMP Acme4321::put_Bandwidth(double Bandwidth)
{
  HRESULT hr = S_OK;

   // Retrieve the cache entry for the Bandwidth property
   CCacheEntry<double>* pEntry = GetOrCreateCacheEntry<double>(_T("IAcme4321.Bandwidth"));

   // If the value is in the cache AND is valid, simply return since we don't need to send the instrument command
   if (pEntry->ContainsValue(Bandwidth, GetModel()))
      return S_OK;

   // If we get this far, then the new value is not in the cache, so we
   // must communicate with the instrument to set the value
   HRESULT hr = io.Printf(_T("SENSE:BAND %.15g"), Bandwidth);

   if (SUCCEEDED(hr))
   {
      // The new value was successfully sent to the instrument, so update the cache
      pEntry->UpdateValue(Bandwidth);
   }

  return hr;
}