A small optical sensor on the bottom allows the vehicles to follow any thick black line made from a marker or crayon on a white piece of paper. Each vehicle includes one black marker a test track operating instructions and 4 "AG13" button batteries. Manufacturered by Bits and Pieces. A wonderful gift for any child Train Engine measures 3" long x 1-3/4" wide x 1-1/2" tall. How these vehicles work is a bit mysterious but we're sure your children will love watching this train drive around and around their drawings.