Galvanic is easy to beat, just tell the examiner you are diabetic and they have to disallow it.
A crafty examiner reinserts control questions along the way. Expected false questions that are often repeated are hard to reset for and give the same response to.
Again it is always highly subjective.
One does not need to “pass” a polygraph, all one must do is screw it badly enough that none of the responses are reliable.
DIA interrogated me for a full day...high pressure with lots of threats...wanting to to know: “how did you do that!?!?”
I told them I had practiced staying calm on a biofeedback machine and did lots of yoga. I was only trying to stay calm.
But the metrics were all over the place. They said they could not even ascertain I was telling the truth when they stated my name as written on my birth certificate.
“Is your name...” appeared to be their control question of last resort.
This was about a week before I was granted TS/SCI/Specat/LIMDIS clearance.