I have an Excel file with formulas in this manner:
=IF(OR(ISERROR(G16),ISERROR(G17)),X16,IF(OR(G16=\"xxx\",G16=\"yyy\",G16=\"zzz\"),Y16,IF(G16=\"333\",\"N\\A\",IF(
FormulaDesk is a free Excel add-in that makes complex formulas more readable and easier to understand without having to rewrite them. It makes creating, editing, debugging and understanding formulas much easier. It has two modes: 'Edit View' and 'Explore View', which can be toggled.
The ‘Edit’ view is an enhanced formula editor, with Intellisense etc. It formats as you type, vertically offsetting nested elements for clarity and understandability.
The ‘Explore’ view presents the formula in a simple nested/rolled-up way, with the simplest top-level view of your formula first, but allowing you to drill-down to nested expressions. This enables you to quickly understand how/why it is returning the current result. Click the green bars (rolled-up results) to drill-down. Alternatively, click the ‘Expand all’, ‘Collapse all’ buttons.
In both views you can hover over various elements (eg: functions, parameters etc) to see a popup with more information, such as definition/description, current value etc. Hovering over a range will display its current value for example.
There are quite a few other capabilities.
[Disclosure: I am the author of FormulaDesk]