Part 2 To underscore the other knowledgeable experts on this bog, finding the error before you replicate is very tough, indeed. It takes time, several sets of devoted eyes to methodically question each algorithm, which unfortunately are written in cells, which are hard to edit. One thing I learned was to use spaces in a cells code… Spaces inside a huge concatenated IF Statement (the type I love to make), have no effect on calculation, but a huge effect on legibility and understanding… Remember, Excel 2007 allows something like 7,000 characters in a cell, so spaces can work… Use Alt Tab to move code to the next line… give yourself a clear line and line up the code so that similar code components are in columns… this really helps when you come back a year later and have no comments to remind you what you wrote… also if you use VBA – to calculate and fill in a cell, be sure you clean that code and leave some narratives as to what you are doing…