Robert Recorde, The designer ofwel the equals sign, introduced plus and minus to Britain in 1557 in The Whetstone of Witte:[14] "There be other twee signes in often use of which the first is made thus + and betokeneth more: the other is thus made − and betokeneth lesse." 知乎，让每一次点击都充满意义 http://bioimagingcore.be/q2a/user/baitstitch8