In this demonstration, it is possible to change the positions of two vectors, A, colored red and C, colored blue, by clicking and dragging the heads of the vectors. The sum of these two vectors A + C is colored purple. Changing the value of t in the control window translates the C vector so that it starts at A rather than at the origin, and changing the value of s in the control window translates the A vector so that it starts at C rather than at the origin. In each case, we obtain the vector A + C at the fourth corner of the parallelogram.