Calculating with integers requires knowledge of calculating with natural numbers as well as calculating with negative numbers. There are also a number of calculation rules to be observed. The expansion of the concept of integers to include negative numbers took place almost simultaneously in different cultures. Rules for calculating with positive and negative numbers were found in a Chinese arithmetic book. The Indians also had different names for positive and negative. Diophant of Alexandria, who lived in the 3rd century AD, gave the following calculation rule for negative arithmetic variables: “Minus times minus results in plus, minus times plus results in minus”. Most of the time, negative numbers were only used as an aid to algebraic intermediate solutions, for a long time they were not recognized as solutions to equations. It was not until Leonardo of Pisa, also known as Leonardo Fibonacci, a negative number appeared as the solution to an equation. It is astonishing that many mathematicians rejected negative numbers until the 16th and 17th centuries. It was not until the late 19th century that a new understanding of negative numbers developed.