This is the web version of a  simple demo program I use to explain the basic core Nucleus solver I wrote in the warm fall of 2005 in Toronto. Back in 2003 my employer 2003 asked me to look into a cloth solver to replace the existing one that we had licensed in Maya. I wrote many prototypes and figured out that what I wrote did more than cloth. To understand what can go wrong I focused on the simplest example of  a dynamic system: a simple oscillating spring. The exact solution for a given energy level and is a circle in phase. What I wanted to explore is what can go wrong when we discretize the path of the spring in phase space. We know that the exact solution is a circle.