Here we see two little (x,y) reference frames, one red and one green. Click the mouse button anywhere on the drawing area to place an object visible from both reference frames. Then click and hold the mouse button down while setting the velocity of the object. Once the object position and velocity are set, click on the Action button to set the display into motion. The velocity of the object as observed from each reference frame is displayed on the drawing area. Click on the Reset button to set up another run.