How to rewrite excel formulas in a readable manner?
You can use Alt+Enter in the formula bar to make your formula multiline. Sadly, no tabs only spaces so it becomes tedious to create and edit. See also
http://www.dailydoseofexcel.com/archives/2005/04/01/excel-formula-formatter/
Naming some of the cells you refer to might make the whole thing more readable
As an example using helper columns, you could shorten the formula with the following
[A1] =VLOOKUP(F16,$M$36:$N$41,2,FALSE)
[B1] =HEX2DEC(W$10)
[C1] =HEX2DEC(W16)
[D1] =HEX2DEC(W17)
then the large formula is shortened to
=IF(OR(ISERROR(G16),ISERROR(G17)),X16,IF(OR(G16="xxx",G16="yyy",G16="zzz"),Y16,IF(G16="333","N\A",IF(G17="333",Z16,IF(D17="",IF((B1-C1)/A1<0,0,(B1-C1)/A1), IF((D1-C1)/A1<0,0,(D1-C1)/A1))))))
This is particularly effective when using volatile functions such as DATE or NOW which you don't want to recalc for every cell when it's the same result.
Whether it's more readable, perhaps not but you can label column headings with appropriate comments