 Representation-As  raises a number of questions when applied in the scientific context. The first concerns the notion of a \(Z\)-representation. While it has intuitive appeal in the case of pictures, it is less clear how it works in the context of science. Phillips and Newlyn constructed an elaborate system of pipes and tanks, now know as the Phillips-Newlyn machine, to model an economy (see Morgan and Boumans 2004 and Barr 2000 for useful discussions). So the machine is an economy-representation. But what turns a system of pipes and tanks into an economy-representation?