How long did it take to wash all the windows in the World Trade Center's twin towers?

A closer view of the top of the North Tower. Look right above the telescope and notice the man standing in an odd looking contraption. That was the automated window washer. The entire thing moved around the top of the building on a track. If you look below the telescope on the bottom right side of the picture you will see the actual washing apparatus going down the side of the building. It took the machine one week to wash all the windows on one side. Thus each tower's windows were washed about every other month.

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