I just posted above about our experience.
My H said he would do anything. I set it up and said I wanted him to take it. He said okay but was apprehensive. He hated every minute of it, said he felt like a criminal, but knew it needed to happen.
I told him that we would go through it no matter what (to forestall incomplete "parking lot confessions") and also that I would believe the results (ditto the "test is wrong" excuse).
The polygrapher explained that it is not pass/fail but shades of grey that he interprets with help from preliminary tests he does on the subject. He considers it over 90% accurate if done correctly.
Afterwards we went to a fancy jewelry store and he bought me the diamond bracelet of my choice, which I now wear every day!