caused by switching the position
of two adjacent digits. Since the resulting error is always divisible by 9, accountants use this fact
to locate the misentered number. For example, a total is off by 72, dividing it by 9 gives 8 which indicates that one of the switched digit is either more, or less, by 8 than the other digit. Hence the error was caused by switching the digits 8 and 0 or 1 and 9.