Sundial

Why it works

A billboard that tells the time. To promote McDonald's breakfast, Leo Burnett Chicago turned a board at Clark and Addison, just west of Wrigley Field, into a working sundial. A metal M fixed along the top edge casts a shadow that sweeps across a row of breakfast items, falling on coffee at six and on a different item each hour after that; at noon the arches' own shadow sits dead centre. The agency brought in a Chicago electrical engineer, Christian Huff, who chose the site because the sun hit it at just the right angle through the morning. It is studied as a landmark of three-dimensional outdoor advertising: no screens or sensors, only geometry, turning a static poster into something passers-by could check every day while quietly reminding them when breakfast ends. It won the Grand Clio for billboards in 2007, and in 2014 it was inducted into the Clio Hall of Fame.