The parallel motion linkage can be used to make things move in the same direction a set distance apart. There are several good examples of these in action. The pantograph is a parallel motion linkage used by electric trains to pick up power from overhead cables. Another use is the pantograph used in drawing to copy sketches. Other uses are in containers such as tool boxes and sewing boxes which open up to reveal multiple shelves and containers which need to be held horizontal.
Parallel motion is only achieved if the levers at opposite sides of the parallelogram are equal in length.