A transposition error is a simple error of data entry that occurs when two digits that are either individual or part of a larger sequence of numbers are accidentally reversed (transposed) when posting a transaction. Although this type of error is often small and unintentional, it can result in huge financial losses in some instances. A transposition error is simply substituting two sequential digits. For example, the number 78 for 87 or 1346 for 1436.