Sean, I download the Mason from your webpage and zip it to C:/appl/Mason. Then I run the mason/start/mason.bat. And add the directory to the ClassPath. However, I went to the C:\appl\Mason\mason\sim\app\tutorial1and2 directory. I run the command such as javac CA.java. The system generates the following error: C:\appl\Mason\mason\sim\app\tutorial1and2>javac CA.java CA.java:6: cannot access sim.engine.Steppable bad class file: C:\appl\Mason\mason\sim\engine\Steppable.class class file contains wrong class: Mason.sim.engine.Steppable Please remove or make sure it appears in the correct subdirectory of the classpa th. public class CA implements Steppable ^ 1 error Could you help me to setup my coding environment? I run it in windows XP. Thank you Best Regards Le Zhang