A nice little excerpt from Thomas Kühne‘s “What is a model?“:

A Copy is not a Model

If I build a car according to an original being precise in every minute detail, I have  not constructed a model but a copy. If I use the copy in a crash test, I have not performed a model simulation but a real test run. Copies neither offer the advantages of models (typically cost reduction) nor their disadvantages (typically inaccuracy with regard to the original).

For an example of an inaccurate model consider an electrician who frequently needs to work out which of several light bulbs in the attic is controlled by a particular switch on story below . The electrician is interested in walking the stairs as few times as possible and figures that bulbs and switches have “on” and “off” states and that all visits to the attic just need to generate a unique “on/off” sequence for each bulb so that it can be matched to the same “on/off” sequence of a switch. For three light bulbs one needs three different sequence which can only be generated with a minimum two visits. While this answer is true for the electrician’s model, it is not for reality. In reality the electrician can figure out the correspondence of three bulbs and switches with just one visit to the attic. Hint: The model dropped the fact that light bulbs not only emit light but heat as well and that it takes a while for a light bulb to completely cool down again…