Mine has been pretty much spot on. However others have said similar to you, and others still have found larger variance.
The struggle I assume is first in the regulation. It’s need to right and perfect.
Also, and here’s another question for Christian’s list (sorry Christian), I have heard chatter about brass being a better facilitator of the resonance phenomenon than gold and a quote to this extent being attributed to FPJ directly.
But it’s chatter, second hand information. However it seems like an odd thing to say (or acknowledge) given that the number of gold movements would likely far outweigh brass.