Page 1 - Check for Errors Study Guide for the Postal Service Exam

General Information

Important Notes

This is part of our test prep for the new cluster of Postal Service Exams that were instituted in April 2019. They are tests #474, 475, 476, and 477. These tests replaced Postal Service Exam #473, which is no longer given and whose scores are no longer valid for Postal Service job applications.

Before you start, be sure you are preparing for the right test content. This section (Check for Errors) is only included in two of the four Postal Service tests (#474 and 476), so you’ll want to be sure you really need to prepare for it. There are other sections that are only present on one test or are in all of the four tests. To be sure you are adequately preparing for the exact test you’ll take, please follow this link and look under “General Information” for more details on each of the four tests and the sections they include. You will find this information or a link to it in all five of our study guides for this test.

What You’ll Be Asked to Do in the Check for Errors Section

The Check for Errors section is included in both tests 475 and 476 and tests your ability to notice fine errors or differences in printed numbers. Both of these tests are given to people applying for jobs in the mail processing and handling categories. They are job types in which a worker needs to note this type of fine detail to route mail correctly.

The questions are presented in groups of four. When you finish those four, you go to the next screen which has four more. Do this again, answer the next four, and you’ll be finished because there are only 12 questions in this test section.

A note about timing on this section of the Postal Service Exam: Like the rest of the test, nothing is timed. However, the instructions for this section will say something like, “Working quickly is in your best interests.” This implies that it may benefit you, in terms of score, to get these questions done as quickly as you can accurately do so.

The task in this section is the same for every single question, and it couldn’t be simpler. You will see two sets of 8-digit numbers. Your job is to determine whether these numbers are exactly alike or if they contain even one difference. If even one number is different, the whole number is different.

The design or presentation may be a little different, but this is the essential content in each one of these questions, with differences in the numbers used, of course. There will be two 8-digit strings of numbers and a place for you to click whether the numbers match exactly or if there is any sort of error (difference) in them. This is the content for one of the questions.


What you’ll actually see on your test is a list of four questions at a time, looking similar to this. Try your hand at these four, then look for the correct answers, below.



  1. Match
  2. Error: 47 in first number is switched to 74 in second number
  3. Error: first number starts 69 and second number starts with 66
  4. Error: last 3 numbers of first are 854 and second are 548

Tips for Success

At first glance, two number groups may look the same, but there are some quick and easy tricks for making sure they are, or discovering they are not.

Divide the long strings into groups of four.—Research has shown that the human eye cannot process more than about four characters at a time effectively, so don’t try for the whole 8-character sequence at once. Check out the first four numbers. Then, if they are the same, try it with the last four.

Either mouth or say each number out loud as you work.—Since you should have found a quiet space to work on your test, it should not bother anyone if you talk to yourself. And it may be worth doing so to get these questions correct. Somehow, forming the numbers with your mouth tends to help your brain identify possible differences more easily—possibly because you’re using more than just the sense of sight.

Once you find one error in a pair, you’re done with that pair.—All it takes is one difference for an “error,” so don’t waste time looking for more. If they’re not the same in any way, the numbers are not the same and you should mark “error.”

Be especially careful if you have problems with reversals.—If you typically struggle with letter and/or number reversals, saying these out loud and being extra careful is important. If four numbers at a time are still too taxing, try two numbers at a time, or even just one. You can also use your fingers, a pencil end eraser, or a stylus to touch each number of both series to see if they match. This may take a bit longer, but you can still work quickly.

Keep up your pace.—No, there’s no time limit, but since the instructions mention a benefit of finishing quickly, just be sure you’re not taking any extra time.

Do any review of your work before clicking on to go to the next group of questions. You will not be able to go back to any previous set of questions after you have moved on.

How You Can Practice

We have some excellent practice for you in the form of free practice questions and flashcards. Also, you can easily construct, or have someone else create, practice pages for this test. It could benefit you to have some recent experience looking at strings of numbers, especially if you don’t normally do so on a daily basis. Practice is also helpful if you struggle with tasks like this.

All Study Guides for the Postal Service Exam are now available as downloadable PDFs