In the middle ages, weight unit (1/4 of quintal; 11, 5 kg); in 1971, Ray Tomlinson used the symbol "@" as "at" (in English "in") to separate the user name of the e-mail server. From Arabic 1575; 1604; 1585; 1576; 1593; (ar-rub, the rubac; "the quarter") with something from the latin ad ("to" or "envelope").