Now that the necks are rough carved it is time to attach them to the Sound boards.
You must do a little whittling and then with an acrylic caul, you position the neck and sound board so that you will have a perfectly straight instrument.
Carefully line up the neck centerline with that center mark at the bottom end of the Sound Board. Then tap in the little brads that go through holes in the caul. Now when you pull the brads out, you have the holes they made for reference. After putting on the glue, you can put it all back together exactly the same.
Check for straightness again with that long ruler-and them clamp it up.