The following rules should be observed in deciding on a time step:

1. Time step * growth rate <= 0.1

In other words, the amount of growth in one time step should be everywhere not more than 10%.

2. The amount by which any part of the mesh rotates in one time step should be not more than about 10 degrees.

3. The change in the concentration of any diffusible morphogen at any point should be not more than 10%.

If the time step is much larger by any of these criteria, the computation may not be accurate, and may be unstable.