  Another broad class of purposes to which computer simulations can be put is in telling us about how we should expect some system in the real world to behave under a particular set of circumstances. Loosely speaking: computer simulation can be used for prediction. We can use models to predict the future, or to retrodict the past; we can use them to make precise predictions or loose and general ones. With regard to the relative precision of the predictions we make with simulations, we can be slightly more fine-grained in our taxonomy. There are a) Point predictions: Where will the planet Mars be on October 21st, 2300? b) “Qualitative” or global or systemic predictions: Is the orbit of this planet stable? What scaling law emerges in these kinds of systems? What is the fractal dimension of the attractor for systems of this kind? and c) Range predictions: It is 66% likely that the global mean surface temperature will increase by between 2–5 degrees C by the year 2100; it is “highly likely” that sea level will rise by at least two feet; it is “implausible” that the thermohaline will shut down in the next 50 years.