When we talk about the design of a piece of hardware, we usually default to observations about its outward appearance–its form, its color, the materials it’s made of. Often, though, that’s only half the equation. For a product like the new Square Reader–a sleek update to the familiar credit card-swiping dongle that’s nearly twice as thin as its predecessor–most of the design work is out of sight. It exists in the meticulous selection and arrangement of the components inside–the delicate stacking of circuitry and silicon that make our gadgets go. In this unseen world, every millimeter shaved is a victory. And in terms of getting tiny things even tinier, the new Square Reader makes for an excellent case study.