During simulation the motion of each of the bodies in the Universe is shown as a moving dot or as a line on the screen. Several vision modes are available. Also during simulation it is possible to move around the perimeter of the Universe using the arrow keys, thereby viewing it from different angles. The second parameter on the command line, in this case 2PLUS1.BDY, refers to a text file specifying the start conditions of the Universe to be simulated. The exact format of this file is described below.
Simulation proceeds immediately after the start condition file has been read.
Key Function Left arrow Move your point of view 5 degrees to the left. Right arrow Move your point of view 5 degrees to the right. 5 degrees up. Down arrow Move your point of view 5 degrees down. Page Up Zoom in Page Down Zoom out 1 Vision mode 1.