The drawing below is from Gustave Eiffel's book describing the tower that bears his name. There are 53 of them in total.
XIII bis. Second floor gallery
Although seeming to be a big mess, this board is an essential element in the plans of the Eiffel Tower. It represents the detailed assembly diagrams between the various structural elements, but also contains a plan of the 2nd floor. This board is very technical.
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