Excel's built in formula auditing tools is and always has been rubbish, sure you may have got used to how they work and feel quite competent/happy with it - but the Explode excel addin will blow your mind!
If you work with excel a lot and you don't use the add in Explode you're in one of two camps:
Explode is pretty old now (but as useful as ever) and the great peops over at XL-Logic.com who authored it have long since taken their website down, but you can still access it from their download page from here, (my mirror,
Update 9-Jun-2016: see my blog post, don't download the addin from google's first hit of Clubfinance Project Finance as is a really old version.
explode.xla from the zip to any folder, then this (for Excel 2007) go to Excel Options, Add-Ins, then 'Manage: Excel Add-Ins', 'Go...'. Broswe to the file you just extracted and you are away.
Just right click a cell containing a formula and select 'Explode...' and you are away. You can then trace both the pecedents and dependants with ease.
Stay tuned for some more excel goodness, I've got a blog post about another super usefull util, Name Manager, coming up.