One problem when gluing a neck is that you have to get the geometry right in both height and lateral at once. In order to keep track of the position laterally, I have made a small manic using the outermost sticks and strings of the stables to make a final fine adjustment of the neck. When gluing, only a very small lateral adjustment is needed, which is anchored when the glue is allowed to dry. You can't really trust that the grip board is straight on the edges, before I did this thing it happened that I was tricked by a crooked grip board when I was aiming for a ruler.
Most of it is clear from the pictures. The two screws can be loosened and the string tightened by hand before they are clamped between the two metal plates.