Browsing links on Brent’s Method I found:
which is well worth a look (plenty of stuff on statistics and Python, with the odd dash of Excel). The link has VBA code for a class based Excel user defined function implementing Brent’s Method to find the roots of non-linear equations. Time permitting, I’ll have a look and compare with my effort
* From a quick survey of the blog, I ‘m not convinced of the daftness of the author, but he should know I suppose.