Microsoft Excel is WRONG!!! Beware...
MS Excel is not designed as an engineering tool. In many cases it is perfectly acceptable to use it as such, but as the original poster so elequently put it...BEWARE. It can be made (read: tricked) into doing lots of different things but at what cost? I know I'm straying from the issue of order of operation, this is just a pet peeve of mine.
If high levels of precision are a priority, you should probably be using a software package designed with complex mathematics and/or engineering in mind. MatLab and MathCAD are two that come to mind, though I'm sure there are a dozen good ones out there.