> Sorry, I must be confused. But wasn't there some issue with radically > changing the size of the time step? e.g. going from 0.01 sec to 1.0 sec > or vice versa? yes ... the issue is that the error correcting velocity would be artificially magnified when switching from a small to large time step (e.g. *10). this issue is on the fix-list. russ. -- Russ Smith http://www.q12.org/