Control-click and drag to zoom in/out.  
  Right-click and drag to translate the camera.  
     
  Click on a particle to select it, drag to move it around.  
     
  O: Add a neutral particle.  
  P: Add a particle of charge +2.  
  N: Add a particle of charge -2.  
  D: Add a dipole (+2/-2 pair).  
  +: Increase the charge on the selected particle.  
  -: Decrease the charge on the selected particle.  
  X: Delete the selected particle.  
     
  ]: Pause the the simulation.  
  I: Show/Hide instructions.