The "holes" in the middle of this one reminded me of buttons. You know the sort, the large "chunky" ones that you find on coats etc.

Today’s Gratitude Item: Integration (as in Calculus). Not only is this a convenient way to work out the “area under a curve”, its also a good topic to teach. Had two classes of it at school today and one of my private students wanted to revise / learn it as well. Turns out that integration can be good for paying bills 🙂