I have a Schon with a warped neck. I used a mirror to conduct this test I rolled the butt back and forth to find where it lifted off the glass. I did this test twice on different mirrors with the same result. I was able to get 1 card to slide down to about 1" past the points, I was able to get 2 cards under it from the points up but a 3rd card was not possible as far out as the end of the joint. With my cheap calipers it take 21 cards to equal .125" giving me about .006" card. Here is an example of how the cards were.