How did the symbols +, – etc originate?

The earliest print appearance of the modern signs seem to come from a book on Mercantile Arithmetic by Johannes Widmann in 1489, used to indicate surpluses and deficits. The + is a simplification of the Latin “et” (comparable to the ampersand – &). Widmann referred to the symbols – and + as minus and mer. According to the ‘Earliest Uses of Various Mathematical Symbols’ website, a book published by Henricus Grammateus in 1518 used the symbols. Robert Recorde, the designer of the equals sign, introduced plus and minus to the UK in 1557 in The Whetstone of Witte.