# Time: tradeoff

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## Choosing a timestep that is short enough to be accurate and yet not take too long to compute

There is a **tradeoff between speed and the accuracy** with which the equation solver can solve the equations. This is feature of all numerical modelling. Continuous time is approximated by a** series of short intervals or steps ( dt)**. With steps that are too long the mesh will grow more than about 2% - an acceptable limit. Very short steps take a long time to compute and can also suffer rounding problems. This is an example of subdividing a rectangular mesh in the region in which curves will develop.

**It still might not be correct because the mesh might be too coarse,** See mesh tradeoffs

**It still might not be correct because the tolerances might be too large,** See tolerance tradeoffs