Hi, This is my first post here. I think my question is relevant to the area of calculus hence posting here. In short: I suck at mathematics after years of trying, and I have a problem that I hope someone can help me with. Full disclosure: this is for a commercial project, so if that is not allowed, my apologies in advance. Imagine I have an irregular 5-sided closed shape (Figure A). I draw a line horizontally through the shape, cutting it into two areas. Let's shade the bottom area, and call this area A. Imagine I now rotate the shape (Figure B), but my line remains in the same position horizontally on the page. How do I compute the new position of the line in order that area A remains constant? How would I compute this line for any angle? Many thanks in advance. MD11.