I was trying to figure out how to set a trailing stop in Excel (I was trying to do something more exotic than what was allowed in IB), unfortunately I kept on hitting up against the problem of circular references. However, I've figured out that all you have to do is go into Tools-->Options, and click on the Calculation tab. Then make sure that the "Iteration" box is checked, and set "Maximum Iterations" to 0 and "Maximum change" to 0.001, and click OK. This will take care of any circular reference error popup windows and the calculation is flawless. This may not be a big deal to 99.9% of the readers out there, but I'm feeling quite satisfied right now.