For example, the octal 7426 minus the octal 4755, directly write the equation, 7426 - 4755, then 6 minus 5 = 1, 2 to 5, 8, 8-5 + 2 = 5, the same reason, 4 because before borrowing After 8, so minus 1 is equal to 3, then borrowing 8,8-7+3=4,7 borrowing 1 change 6,6-4=2, the result is 2451