The jitter logic in the simulator is not correct

[bennage]

The jitter logic is always adding to the interval. Instead it should be plus or minus.
For example, if we say that the event frequency can vary by 2% then it will always increase the frequency by a random value between 0 and 0.02. We really want it to add a value betwee -0.02 and +0.02.

See b99a22c for details.