Use the balance to find defective products. First, divide the product into two equal piles, and then put these two piles into two trays of the balance to see which end of the balance is inclined. The defective products are in the inclined pile (provided that the defective products are lighter than ordinary products, and if they are heavier than ordinary products, they are in the sinking pile). After that, take out the pile with defective products, divide it into two piles, and repeat the above operations to find out the defective products.