Given that the equatorial circumference of the Earth is about 40 075 km and that c is about 300 000 km/s, the theoretical shortest time for a piece of information to travel half the globe along the surface is about 67 milliseconds. When light is traveling in optical fibre (a transparent material) the actual transit time is longer, in part because the speed of light is slower by about 35% in optical fibre, depending on its refractive index n. Straight lines are rare in global communications and the travel time increases when signals pass through electronic switches or signal regenerators.