One of the earliest uses of measurements was their well-known role in trade, where the ability to use rudimentary measures of weight not only made it possible to barter with food and raw materials but also enabled things to be built and manufactured. The simple ability to measure the length of things by means of specific units, combined with some elementary arithmetic and geometry, enabled craftsmen to design and construct things such as cathedrals, castles, bridges, houses, musical instruments, furniture, tools, and clothes. Reflecting further upon this observation, we come to realize that it is the ability of humans to measure and apply basic mathematics that makes it possible to design things at all. Designers can work out on paper or by means of computer simulations how to build something that does not yet existhow to construct, say, a building or a ship whose size matches our needs and is stable and strong enough, while also satisfying our aesthetic ideals. More than this, though, our ability to measure and calculate makes subsequent epistemic uses of the design possible. In the actual process of construction, the epistemic uses of a design include, for instance, calculating the quantity of materials to be used and the dimensions of the component parts.