Should You Pencil Mark Your Sudoku Puzzles?

This was recorded during Sudoku Week 2020 on October 6th. Transcript below.

Hey everybody. Welcome to our final session on our marathon question and answer today where we’re answering, “Should you Pencil Mark your Sudoku Puzzles?” A lot of controversy related to that.

So we are in the middle of Sudoku week and all this week is a celebration of all things Sudoku. Today, we were doing all these question and answers, all these questions that we get from you, our loyal fans. And I want to thank you for joining us and for commenting and helping us make this a better time. And I want you to enjoy it as well. So I want you to go to You can see the link right there and check it out.

Sign up for our giveaway, but when you do sign up, you’ll also continue to get the emails, if you’re not already, about all of the activities that we have going on this week, all the puzzle solving, all the techniques, everything that we’re releasing this week, so that you can be a better Sudoku player and you can have a lot more fun.

So again, today’s topic is all about pencil marking and “should you pencil mark your Sudoku puzzles?” Because like I said, there’s some controversy and we have strong opinions on both sides. I think one thing that caught me off guard, right? When I first started teaching people how to play Sudoku I was telling somebody how to do this. He says, “I don’t pencil mark anything”. You know, he solves Sudoku. “I don’t pencil Mark it at all. I want to exercise my memory.” It kind of surprised me. And we’ll talk about that a little bit later.

Then we actually had a recent email from another viewer who says, “I think pencil marking is cheating”. So he doesn’t want to pencil mark because it’s cheating.

I will say that most people use and they ascribed to this thing, what I call the brute force method. Everybody else calls it solving. I call it brute force because, and I have an example of it right up here in the corner. This is, ignore the rest of it, this is all the little pencil marks that you write in here. Everybody, if you’re on here and you’ve known me for quite a while, you are well aware of the brute force. And I’ve described this to you, but this is what I talk about, this is where you write little pencil marks in every space that’s empty. And every pencil mark that’s there is all the possible numbers that could go in that space. Then you repeat that through the whole board.

All the apps that you have that you run on your computer or tablet or whatever, they all use this. You can do it with a push of a button. You can have the whole thing filled in. And I think most of the other people that teach on YouTube, for example, the other Sudoku guys, gals and gurus out there they start off a puzzle. That’s showing with that throughout the whole puzzle. That’s how they solve.

So let’s look at that. There’s actually, there’s this kind of a continuum. There’s the folks on one hand that say, “Hey, we shouldn’t pencil mark at all.” For whatever reason they think is cheating or they think they’re going to work on their memory because of that. And we have the other end of the spectrum, which is the brute force. Sudoku Professor is somewhere in between actually, you know, I’ll show you how to do it, it’s actually shown on the puzzle here, but I’ll talk about more of that. We’re in between there on the spectrum.

So again, I’ll just repeat for those who are new to Sudoku Professor. We don’t do the brute force and the reason we don’t do Brute Force is because it puts too much extraneous data on the board. And by putting all of that extraneous data, the things that don’t matter, the things that aren’t going to help you, it actually hides the good information that you would see that could actually help you solve the puzzle. I think it has other things. I think it reduces the fun, if not eliminates the fun, it’s exasperating there’s a lot of reasons to avoid it. And I’m going to give you some reasons, what to substitute.

But then again, we have the other people that are all the way over on the “no pencil marking” end of the spectrum. Now what’s interesting about this is again, they often refer to the memory, that “I’m going to try to I’m going to try to remember everything that’s on the board”.

The problem is that that’s not going to work very well for you. And there’s scientific proof of, or I guess I should say scientific evidence. These people talk about the scientists that study the brain and memory and cognition and everything like that, they realize that when you’re doing Sudoku, that you’re engaging a part of your brain, a part of your memory called working memory.

Now working memory, it’s sort of like short-term memory and some people kind of conflate the two. There is a distinction, short-term memory, it’s more like the storage of that memory. Whereas working memory is, like you would imagine, you have a memory of it and you’re actually manipulating it. You’re actually working with the things that you’re trying to remember.

The problem with working memory is that it’s actually very small. There’s a lot of evidence to show that you have, the average person has the ability to remember about seven bits of information, seven chunks of information. It could be seven numbers in like a phone number or something like that. Or it could be seven things on a Sudoku board, or it could be seven other pieces of information. However it’s chunked up. So on average, it’s about seven.

Some people, depending on the situation and the type of things that you’re trying to remember, it may be four, maybe eight or 10. And, you know, some people have either trained their brain or they’re actually geniuses, you know, or have some sort of like savant ability and their memory extends way beyond that.

But for the rest of us, you know, the normal people, you’re really limited about seven bits of information. And it’s sort of like when you, I can kind of imagine when you’re trying to fit one more piece in on one end, something’s gonna fall out the other end. And that’s what your working memory does. So what happens when you don’t put any pencil marks on the board, you’re trying to use your memory, you’re really using your working memory, which is a great thing to exercise, but you’re not really going to be able to remember that much.

Normal people under normal circumstances don’t have the capacity to remember much. So what you end up doing is you end up redoing the logic a lot. That’s what happens. You end up not remembering where eight was able to go in this box or six or whatever, and so you end up redoing that logic multiple times.

Again, we split the difference here at Sudoku professor, and so we put useful information. So what you see up here is brute force. Obviously you would know what the puzzle would look like if it had no pencil marks on it. And I’ve done a little bit of pencil marking on the rest of the board to show you how we are very strategic in the pencil marking that we do, that allows us to see the good information.

Part of the pencil marketing, for example, that I’ve done already allows me to see that One could only go in these two spaces right here on this box right here. And that Three can only go in these two spaces right here. Just because of the pencil marking that I’m doing and that I’m limiting it. Okay.

Those are called double row eliminations. That’s a junior level technique that we teach. But I want you to think about, let’s think about it a different way. Let’s say, well, if you’re on either end, either on the end of you don’t believe in any pencil marking or you believe in pencil marking everything and brute forcing it. Let’s talk about that.

So let’s imagine you have two students in class. They’re sitting next to each other. They’re just average students. We’re not talking about neither one is exceptional. You’ve got John and you’ve got Mary. They’re both interested in the subject that the professor down front is teaching. They’re both paying attention.

Now, John, he’s the tough guy. He’s going to sit there and he says, “I’m not going to bother to take notes. I’m going to listen carefully, and I’m going to remember what I need to know.”

Mary, on the other hand is sitting there with a notebook open and she is listening. And she’s trying to determine what is it that the professor is emphasizing, what’s important, let me take notes about that, let me write this stuff down. She’s not trying to write everything down verbatim. She’s just trying to write down the important things, right?

So now who, I’m going to ask you a question, who do you think is going to do better when the exam comes around? Now Mary, when the exam comes, you know, we’re talking about weeks have gone by many, many lectures have gone by and they’ve had all this stuff and John has not taken a single note. He’s paid attention, but he’s not taking a single note. Mary has taken notes, a lot of notes.

So the night before the exam, Mary is reviewing her notes, she’s recalling all of this stuff. What can John do? What’s John gonna do? Well, he can’t recall everything. I mean, even if he has a really good memory, he’s not going to recall the content of every lecture. He’s probably not going to be able to recall even a lot of the important points, because what’s really important?

I mean, he’s trying to pay attention, but what was emphasized? I don’t know. Again, he’s just got average memory. We’re not even talking about whether it’s short-term or long-term or working memory. We’re just talking about just trying to remember. So he can’t remember. I don’t think anybody could expect John to be able to remember and recall. So what is he going to do? He’s going to end up resorting to going back to the textbook, which has the entire subject in the textbook.

Now, a lot of classes that you probably attended and I attended, the teacher didn’t teach the entire textbook. The teacher taught parts of the text, skipped, moved, you know, didn’t teach the details of everything. Skipped, moved around, basically got the highlights or got the important things and things like that. Occasionally you did go to a class that did teach the textbook in the end.

But the point of it is, is that John is going to sit there and he’s going to break open the textbook. That’s like resorting to brute force. He’s now looking at everything about the subject that could have been covered in the class. Most of which is not going to be on the exam. That’s what we get with brute force. We have all of this extra data, most of which doesn’t matter. So for example, if you look up here, nine can go in every space that’s empty. How does that help us to figure out where nine goes? It doesn’t, okay. That’s like opening the book.

Who do you think is going to do better on the exam with less effort? I think that both of us would agree that it’s Mary. So what we’re doing when we do our things, when we reduce, when we make notes of where a number could go into spaces within a box or when we make notes of double-doubles and other things like that that we can find. And we we emphasize that good information.

We are taking notes. We’re like Mary, we’re taking notes of the good stuff. And we’re not trying to remember everything, but at the same time, we know that that we’re, since we’re not putting everything, there are some things that we either need to recall, or we might need to redo some logic. But we’ve got the important stuff on there. And we’re able to use that good stuff, it’s not cluttered up with things that we don’t need. We’re able to use that good stuff to help us solve the rest of the puzzle.

If you want to learn how to do this type of pencil marking, it’s real easy. You just need to sign up for our lessons, but I’ll tell you what the best way to do right now is to, is to get involved in what we’re doing this week. So if you sign up for the giveaway, you will be getting the emails about all the rest of the events and the videos and other information. The other learning, teaching material that we’re doing for the rest of this week, you’ll be getting emails. We’re actually doing a webinar tomorrow. We’re going to go over four puzzles and invite our club members. I’m going to show you where they’re stuck, what we can do to help them get past that. And you’re going to learn from that. And there’s a lot more coming out later this week.

So if you just go to, you can sign up there. You can sign up for a big giveaway. You could be a winner. You could be that grand prize winner. And I will be drawing that on Saturday. And at the same time, again, you’ll be signed up for the emails that you’ll get for the rest of the week here on, on all the things, all the great things that we’re doing for Sudoku week. Well, thanks a lot. I hope this helps.

We wanna reduce our pencil marking to the to note taking and we want to be Mary. Don’t be John, be Mary, you know. So get out there and solve more Sudoku, learn how to do it. I’m here to teach you. That’s what Sudoku week’s all about. And sign up again, go to our and sign up for their Sudoku player’s dream giveaway sweepstakes, and I’ll see you tomorrow.

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Robert Barker