Not one sold on here I hope. I'm out of the loop for current models--mine is the SCADA RSG-4. It works well and reliably.
So what are you expecting the zapper to do which will show it's working? Again, READ Dr. Clark's book for proper usage and what to expect. It will tell you what are reasonable expectations.
If you've got it to cure a disease, there's usually an infection involved to which I found zapping was kinda slow on doing, (it's much faster on parasites than the pathogens, as the pathogens reproduce much faster) so check out what herbs I used instead.
'Trying the zapper on an illness to see “if it works” is not useful. Your symptoms may be due to a non-parasite. Or you may reinfect within hours of zapping.' page 28, CFAD