 Frigg and Nguyen (2016: 227–8) argue that in order to turn an object \(X\) into a scientific model, it must be interpreted in the appropriate way (note that they do not use “interpretation” in the way that Contessa uses it, as discussed above): properties that \(X\) has, qua object, are paired up with relevant \(Z\) properties and for quantitative properties, i.e., properties such as mass or flow, which take numerical values, there needs to a further association between the values of the \(X\) property and the values of the \(Z\) property to which it is mapped. In the case of the Phillips-Newlyn machine, for example, hydraulic properties of the machine are associated with economic properties and a rule is given specifying that a litre of water corresponds to certain amount of a model-economy’s currency (Frigg and Nguyen 2018).