Hi, I have been experimenting with EJS and it has been quite exciting. However, when I run into problems I do not have any one in the office to turn to. :-( My two big problems are : 1) I wrote a program where I could set the initial trajectory of a body which is subject to gravitational pull towards a fixed point in the centre. So I hope to simulate the different outcomes when the initial velocity is changed (like the newton's cannon). So I set up the acceleration, and use the ODE to work out the velocity and position vector for me. (dvx/dt=ax and dx/dt=vx and so on). However, the outcome has a little error which accumulates after every round. If I changed the time step to a very small number I can eliminate this error but the simulation becomes painfully slow. I tried changing the method used for solving the ODE and none worked. Can anyone tell me how to solve this problem? 2) One thing I commonly want to do is to have two objects in one drawing canvas. Each object has all sorts of arrows associated with it. I find it a chore when making another copy of the same object. I have to copy and paste every arrow. Is there any better way? Thanks in advance. Regards kahhean