When was Unix epoch time revised from 1971 to current 1970 value?
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According to the first edition [Unix Programmer's Manual][1], Unix time is defined as "the time since 00:00:00, January 1, 1971, measured in sixtieths of a second"

When did this change to its current value of midnight (UTC), January 1, 1970?


  [1]: http://cm.bell-labs.com/cm/cs/who/dmr/pdfs/man22.pdf