Today’s invention is a cake cutter for disputatious, geeky families.
It consists of a rectangular, plastic sheet which is flexible in one direction but not in the other. This is fitted to a graduated metal bar a-b. At points a and b the sheet can be slid through a block at right angles to the bar and locked in place. a is slid towards c initially to correspond to the diameter of a particular cake.
This allows the sheet to always take up the shape of two semicircles. Moving b towards c in steps of 1/n th the diameter, produces n equal-size pieces with interesting shapes.
Actually, I’d like to create a cookie or cake cutter employing a visual illusion eg
http://en.wikipedia.org/wiki/Ebbinghaus_illusion
Thus when people chose the ‘big’ piece, they could get their come-uppance.