 As shown in the example, the multiplicand and multiplier are written above and to the right of a lattice, or a sieve.It is found in Muhammad ibn Musa al-Khwarizmi's "Arithmetic", one of Leonardo's sources mentioned by Sigler, author of "Fibonacci's Liber Abaci", 2002.The pictures on the right show how to calculate 345 × 12 using lattice multiplication.