The low 3 digits of the addends are effectively lost. Such compressors can be used to speed up the summation of three or more addends. Given "N" addends, "portioning" concerns the relative contribution of the addends to their sum. The two numbers being added together are called "addends". If the addends are exactly three, the layout is known as the carry-save adder. Unlike addition on paper, addition on a computer often changes the addends. On the ancient abacus and adding board, both addends are destroyed, leaving only the sum.