Abacus, or table of Pythagorus, abacus Pythagoricus, was a table of numbers for the purpose of learning the principles of arithmetic more easily; this table was called the table of Pythagorus because he it was who invented it. [1]

It is probable that the Pythagorean table was nothing other than what we called the multiplication table.See Table of Pythagorus.

Ludolphe [2] has given methods to do multiplication without the help of the abacus or table: but they are too long and too difficult to be used in ordinary operations. See Multiplication.

1. The expression “table of Pythagorus” has been used in many other languages, including Italian, Russian, and English (e.g. John Farrar, An Elementary Treatise on Arithmetic, Taken Principally from the Arithmetic of Silvestre François Lacroix [Cambridge: Hilliard & Metcalf, 1825], p. 17; Farrar, an American, was Professor of Mathematics and Natural Philosophy at Harvard University from 1807 to 1836; he is better known today for having developed the modern concept of a hurricane). Farrar and Lacroix are part of a line of mathematicians traceable directly to d’Alembert and his contemporary and fellow Encyclopédie contributor Charles Bossut.

2. Ludolph van Ceulen, 1540-1610, was a German-Dutch mathematician known as a prodigious calculator. He spent much of his life refining the value of π. In 1596 he extended Adrien Romain’s fifteen-decimal value (published in 1591) to twenty decimal places in Van den Circkel (‘On the Circle’), essentially by continuing the geometric method first proposed by Archimedes in the 3rd century BCE. He later expanded this to thirty-five decimal places: 3.14159265358979323846264338327950288..., a result that was not surpassed for thirty years. At Ludolph van Ceulen’s request, after his death the “Ludolphine number” was engraved on his tombstone.