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For 20 years, the Sears Tower held the record for the world’s tallest building. Completed in 1973, the 110 stories high building is almost half a kilometer tall. And it still holds the record for having the world’s highest antenna. John Zils, structural engineer and designer of this mega-structure shares some of the secrets about the tower . And get a behind-the-scenes look at some of the various systems and controls that are vital to the building, like security monitoring, the elevators, and the water and power distribution to the various levels, and even the machines that cleans the windows.