The evolution of Columbia's elevator light curtain. Virtually everyone who has ridden an elevator over the past several decades knows the feeling of his or her person, children, pets and/or possessions being annoyingly bumped by an automatic door that withdraws upon contact by the mechanical shoe, or buffer, at the door's edge. Many people take advantage of the way these work by using them to hold the car for delayed passengers or to load/unload belongings on a particular floor, inconveniencing others up and down the line.
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