The top of this instrument presented some interesting challenges. In the following paragraphs, I refer to the image above.

Mainly, there was the big V-shaped shrinkage crack down the middle (black). I thought I would just have to plane the sides (it's all but impossible to do a good job of fitting a piece of wood to a natural break) and fill it with new wood. As always, I didn't like that idea because (a.) cracks are never straight, neither along their length nor from the outer to inner surfaces of the wood, so it always requires enlarging them to make them straight, and (b.) new wood never matches old wood perfectly. But over the course of my multi-volume effort to try and flatten the top, all the joints had let go. One of them was near the bottom half of the big crack, just to the right of it (blue line). This resulted in the piece between the crack and the joint being detached and free from the rest of the top. (I should say from the rest of the pieces of the top, at that time.)

I realized that when I took this little piece out, the halves of the long top part of the big crack mated back together nicely. And when I put this piece against the shorter bottom part of the crack, the same was true. So I decided to plane the already-straight joint edge of this small piece at an angle that would make everything come back together (red dotted line). Both the angle and the amount removed had to be perfect, so I took the precaution of making sure I was in perfect mode when I did it. (Actually, I settled for really, really careful mode.)