Robert Recorde, The designer of the equals sign, introduced plus and minus to Britain in 1557 in The Whetstone of Witte:[14] "There be other 2 signes in often use ofwel which the first is made thus + and betokeneth more: the other kan zijn thus made − and betokeneth lesse." http://www.drugoffice.gov.hk/gb/unigb/nl.wikipedia.org/wiki/Kwaliteit