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 twee signes in often use ofwel which the first kan zijn made thus + and betokeneth more: the other is thus made − and betokeneth lesse." http://www.drugoffice.gov.hk/gb/unigb/foliemolie.nl/