The book on the Internet Archive: https://archive.org/details/101unuselessjapa00kawa https://archive.org/details/101unuselessjapa00kawa I remember seeing this

The book on the Internet Archive: https://archive.org/details/101unuselessjapa00kawa https://archive.org/details/101unuselessjapa00kawa I remember seeing this book as a kid. The "perfect cake cutter" (p. 96) stuck with me–two knives on a protractor so you can measure the correct angle. There's also a cutting board with a hole in it (p. 109) to facilitate transfer of ingredients into a pot, which sounds like it would be a successful product.