Actually, the 666 comes from an interpretation of the "Book of Revelation".
Otherwise, I agree that it is a good frequency and is include in one of my new models of zapper that is currently on test. However, I do not rely entirely on that frequency as my data analysis shows that there are things that it misses.
As an example, 666 seems to have little effect on Basal Cell but frequencies close to the following work extremely well. 2116, 2280,
Also, 666 does not appear to help with non-Hodgkin's Lymphoma but 2008, 2004, 2012, 2116, 2128 ...
Gotta love that 7.83 or some like the 15.66 but somehow round it down to 15.0 ( Croft ).