Lattice multiplication

Lattice multiplication is a pencil-and-paper method for multiplying two multi-digit numbers using a grid. It is also called the Italian method, the Chinese method, gelosia multiplication, sieve multiplication and shabakh, among other names. A grid is drawn with one column for each digit of the first number and one row for each digit of the second, and each cell is split by a diagonal. Every cell receives the product of its column digit and row digit, with the tens digit above the diagonal and the units digit below. The digits along each diagonal are then added from the bottom right, carrying into the next diagonal, and the answer is read off the left and bottom edges. In the worked example, 58 times 213 gives 12354. The method is mathematically identical to long multiplication but splits the work into smaller steps, which some people find easier. It had arisen by medieval times, appears in Indian, Arabic and Italian sources, and is still taught in some curricula.