growthRateTolerance property
The amount more or less than the set growthRate that the circles can grow and shrink.
This is used to give the circles a bit of randomness in their growth rate.
For example, if growthRate is 20.0 and growthRateTolerance is 5.0,
the circles can grow and shrink at a rate of anywhere from 15.0 to
25.0.
The default value is 0.0.
Implementation
final double growthRateTolerance;