Doing complex modelling in Excel is not a good idea. There is no way to do proper software engineering, so bugs are common and hard to find. For examples, see<p><a href="http:&#x2F;&#x2F;www.eusprig.org&#x2F;horror-stories.htm" rel="nofollow">http:&#x2F;&#x2F;www.eusprig.org&#x2F;horror-stories.htm</a>