Telephone crossbar switch, Swedish Ericsson, 1921
1921
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1922
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1922-1923
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1920-1925
circa 1920
2000-100 BCE
1924
1934
circa 1920
1955; 1830
1921
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circa 1920
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1990-96
1922-1925
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1920-1922
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circa 1920