Lattice Multiplication
Lattice (Indian) multiplication is written using a prepared grid.
If we want to calculate $29 × 4$, we write the results of multiplying the individual digits into the diagonally divided cells. In our example, $9 × 4 = 36$ and $2 × 4 = 8$. If the result of multiplying two digits is less than 10, it is useful to write 0 in the tens place for clarity, as shown in the following picture.
Once all the digits have been multiplied, we add the numbers along the diagonals, working from right to left. We write down the ones and carry the tens to the next diagonal. The first diagonal contains only 6, but the next one gives $3 + 8 = 11$. We write 1 in the lower (yellow) cell and carry the other 1, representing one ten, to the next diagonal (white) column, where $0 + 1 = 1$. The digits that appear in the bottom row after adding form the final result of the multiplication. The result is 116.
