For example, subtract 4755 from octal 7426, and write the equation directly, 7426 - 4755, then 6 minus 5 = 1, 2 is smaller than 5, so we borrow 8, 8-5+2=5, similarly, 4 has been borrowed from 8 before, so minus 1 equals 3, and then we borrow 8, 8-7+3=4, 7 becomes 6 after borrowing 1, 6-4=2, and the result is 2451