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Calculate Powers of 2 In Your Head!

Published on Sunday, October 26, 2014 in , , ,

Ptkfgs' Doubling Cube imageEarlier this year, I posted about calculating powers of e in your head, as well as powers of Pi.

This time around, I thought I'd pass on a method for calculating powers of a much more humble number: 2. It sounds difficult, but it's much easier than you may think!

BASICS: For 20 up to 210, you'll memorize precise answers. For answers to 211 and higher integer powers, you'll be estimating the numbers in a simple way that comes very close.

First, you must memorize the powers of 2 from 0 to 10 by heart. Here they are, along with some simply ways to memorize each of them:

Problem   Answer    Notes 
  20    =     1     Anything to the 0th power is 1
  21    =     2     Anything to the 1st power is itself
  22    =     4     22 = 2 × 2 = 2 + 2
  23    =     8     3 looks like the right half of an 8
  24    =    16     24 = 42
  25    =    32     5 = 3 + 2
  26    =    64     26 begins with a 6
  27    =   128     26 × 21
  28    =   256     Important in computers
  29    =   512     28 × 21
  210   =  1024     210 begins with a 10
Take a close look at 210, which is 1024. It's very close to 1,000, so we're going to take advantage of the fact that 210 ≈ 103!

When multiplying 2x × 2y, remember that you simply add the exponents together. For example, 23 (8) × 27 (128) = 27 + 3 = 210 (1024). Similarly, you can break up a single power of 2 into two powers which add up to the original power, such as 29 (512) = 26 + 3 = 26 (64) × 23 (8).

TECHNIQUE: We'll start with 215 as an example.

Start by breaking up the given power of 2 into the largest multiple of 10 which is equal to or less than the given power, and multiply it by whatever amount is leftover, which will be a number from 0 to 9.

Using this step, 215 becomes 25 + 10, which becomes the problem 25 × 210.

For an powers from 0 to 9, you should know by heart, so you can convert these almost instantly. In the example problem we've been doing, we know that 25 is 32, so the problem is now 32 × 210.

Now we deal with the multiple of 10. For every multiple of 10 involved, you can replace 210 with 103. With our problem which is now 32 × 210, there's only a single multiple of 10 in the power, so we can replace that with 103. This turns our current problem into 32 × 103.

At this point, it's best to represent the number in scientific notation. In this feat, that simply refers to moving the decimal point to the left, so that the left number is between 0 and 10, and then adding 1 to the power of 10 for each space you moved the decimal. Converting to scientific notation, 32 × 103 becomes 3.2 × 104.

That's all there is to getting our approximation!

How close did we come? 215 = 32,768, while 3.2 × 104 = 32,000. I'd say that's pretty good for a mental estimate!

EXAMPLES: Over 6 years ago, I related the story of Dr. Solomon Golomb. While in college, he took a freshman biology class. The teacher was explaining that human DNA has 24 chromosomes (as was believed at the time), so the number of possible cells was 224. The instructor jokingly added that everyone in the class knew what number that was. Dr. Golomb immediate gave the exact right answer.

Can you estimate Dr. Golomb's answer? Let's work through the above process with 224.

First, we break the problem up, so 224 = 24 + 20 = 24 × 220.

Next, replace the smaller side with an exact amount. In this step, 24 × 220 becomes 16 × 220.

Replace 210x with 103x, which turns 16 × 220 into 16 × 106.

Finally, adjust into scientific notation, so 16 × 106 becomes 1.6 × 107.

If you know your scientific notation, that means your estimated answer is 16 million. Dr. Golomb, as it happened, had memorized the 1st through 10th powers of all the integers from 1 to 10, and new that 224 was the same as 88, so he was able to give the exact answer off the top of his head: 16,777,216. 16 million is a pretty good estimate, isn't it?

Below is the classic Legend of the Chessboard, which emphasizes the powers of 2. In the video, the first square has one (20) grain of wheat placed on it, the second square has 2 (21) grains of wheat on it, with each square doubling the previous number of grains.



The 64th square, then, would have 263 grains of wheat on it. About how many is that? I'm going to run through the process a little quicker this time.

Step 1: 263 = 23 + 60 = 23 × 260

Step 2: 23 × 260 = 8 × 260

Step 3: 8 × 260 ≈ 8 × 1018

While 263 is 9,223,372,036,854,775,808, our estimate of 8,000,000,000,000,000,000 works.

TIPS: If you're really worried about the error, there is a way to improve your estimate. Percentage-wise, the difference between 1,000 (103) and 1,024 (210) is only 2.4%. So, for every multiple of 10 to which you take the power of 2 (or every power of 3 to which you take 10), you can multiply that by 2.4% to get a percentage difference. You can then multiply that percentage difference by your estimate to improve it.

Just above, we converted 263 into 8 × 1018. Since we started with six 10s, our percentage difference would be 6 × 2.4%, or 14.4%. In other words, our estimate of 8 × 1018 could be made closer by adding 14.4% to 8.

Assuming your comfortable with doing percentages like this in your head, 8 increased by 14.4% is 8 + 1.152 = 9.152, so our improved estimate would be 9.152 × 1018. Considering the actual answer is roughly 9.223 × 1018, that's quite close!

Practice this, and you'll have an impressive skill with which to impress family, friends, and computer geeks!

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100 Years of Martin Gardner!

Published on Tuesday, October 21, 2014 in , , , , , ,

Konrad Jacobs' photo of Martin Gardner“Martin has turned thousands of children into mathematicians, and thousands of mathematicians into children.” - Ron Graham

100 years ago today, Martin Gardner was born. After that, the world would never again be the same.

His life and his legacy are both well represented in David Suzuki's documentary about Martin Gardner, which seems like a good place to start:



As mentioned in the snippets last week, celebrationofmind.org is offering 31 Tricks and Treats in honor of the Martin Gardner centennial! Today's entry features a number of remembrances of his work in the media:

Scientific American — “A Centennial Celebration of Martin Gardner”

Included in the above article is this quiz: “How Well Do You Know Martin Gardner?”

NYT — “Remembering Martin Gardner”

Plus — “Five Martin Gardner eye-openers involving squares and cubes”

BBC — “Martin Gardner, Puzzle Master Extraordinaire”

Guardian — “Can you solve Martin Gardner's best mathematical puzzles?”, Alex Bellos, 21 Oct 2014

Center for Inquiry — “Martin Gardner's 100th Birthday”, Tim Binga
There are quite a few other ways to enjoy and remember the work of Martin Gardner, as well. The January 2012 issue of the College Mathematics Journal, dedicated entirely to Martin Gardner, is available for free online! The Gathering 4 Gardner YouTube channel, not to mention just searching for Martin Gardner on YouTube, are both filled with enjoyable treasures to be uncovered.

Here at Grey Matters, I've written about Martin Gardner quite a few times myself, as I have great respect for him. Enjoy exploring the resources, and take some time to remember a man who has brought joy, wonder, and mystery to the world over the past 100 years.

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Even More Quick Snippets

Published on Sunday, October 12, 2014 in , , , , , ,

Luc Viatour's plasma lamp pictureIt's time for October's snippets, and all our favorite mathematical masters are here to challenge your brains!

• I'm always looking for a good mathematical shortcut, in order to make math easier to learn. More generally, I'm always looking for better ways to improve my ability to learn. I was thrilled with BetterExplained.com's newest post, Learn Difficult Concepts with the ADEPT Method.

ADEPT stands for Analogy (Tell me what it's like), Diagram (Help me visualize it), Example (Allow me to experience it), Plain English (Let me describe it in my own words), and Technical Definition (Discuss the formal details). This is a great model for anyone struggling to understand anything challenging. This is one of those posts I really enjoy, and want to share with as many of you as I can.

• If you enjoyed Math Awareness Month: Mathematics, Magic & Mystery back in April, you'll love the 31 Tricks and Treats for October 2014 in honor of the 100th anniversary of Martin Gardner's birth! Similar to Math Awareness Month, there's a new mathematical surprise revealed each day. It's fun to explore the new mathematical goodies, and get your brain juices flowing in a fun way!

• Over at MindYourDecisions.com, they have a little-seen yet fun mental math shortcut in their post YouTube Video – Quickly Multiply Numbers like 83×87, 32×38, and 124×126. As seen below, it's impressive, yet far easier than you might otherwise think:



They've also recently posted three challenging puzzles about sequence equations that you might want to try.

• If that's not enough, Scam School's latest episode (YouTube link) at this writing also involves three equations. If you have a good eye for detail, you may be able to spot the catch in each one before they're revealed:



That's all for this October's snippets, but it's more than enough to keep your brain puzzled through the rest of the month!

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Convert Decimal to Any Base 2 - 9

Published on Sunday, October 05, 2014 in , , , ,

LaMenta3's binary pillow photoAbout 2 years ago, I posted about Russian/Egyptian multiplication, and included a technique for mentally converting decimal (base 10) into binary (base 2).

Recently, Presh Talwalkar covered this same technique on his Mind Your Decisions blog. I've only just realized that with a little modification, this technique can be used to quickly and mentally convert decimal to any base 2 through 9!

We'll use the Mind Your Decisions binary conversion video as a starting point. It's less than 3 minutes long, so it's a quick study:



In both my original Power of 2 post and the above video, the idea of ignoring the remainder is emphasized. Funnily enough, changing the technique to focus on the remainder makes this basic idea much more usable. If you remember division problems with answers like, “22 ÷ 6 = 3 remainder 4”, that's the type of division we'll be using in this post.

The first step is simply to take the given number and divide it by whatever base you're using, so that you have a quotient and a remainder. For a starting example, we'll convert the decimal number 84 into base 5. 84 ÷ 5 = 16 (the quotient), remainder 4.

The second step is to write down the remainder. In our example, we'd simply write down the 4.

Step 3 is to divide the quotient by the base again. This time, we'd work out 16 ÷ 5 = 3 remainder 1.

Step 4 is to write down this remainder to the immediate left of the previous remainder. Writing down the 1 to the immediate left of the 4 gives us 14.

Repeat steps 3 and 4 until you get a quotient of 0, at which point, you've got your answer! Finishing up our example, we'd use our current quotient of 3, divide that by 5, getting an answer of 0 remainder 3, write the 3 down to the left of the previous remainders, giving us 314. Since our quotient is 0, we also know we're done! Checking with Wolfram|Alpha, we see that 84 in base 5 is indeed 314!

TIP #1: Once your quotient is a number less than your base, you can simply write that to the left of the remainders and know you're done. In the above example, once we got down to 3, and we realize this is less than 5, we know this is the final step. Because of this, we can simply write the 3 down and stop.

In short, as long as you're given a decimal number and a base by which you're comfortable dividing that number, you can convert that number to that base in your head with little trouble. Not surprisingly, knowing division shortcuts and divisibility rules can be of great help here.

What about 147 (in base 10) to base 4? As long as you realize that the closest multiple of 4 is 144, and that you can handle 144 ÷ 4 in your head, the rest of the conversion shouldn't be a problem. 147 ÷ 4 = 36, remainder 3. Write down the 3, and then work with 36. 36 ÷ 4 = 9, remainder 0, so write the 0 to the left of the 3 (03), and work with 9. 9 ÷ 4 = 2, remainder 1. Write down the 1 to the left of the previous remainders (103). Tip #1 above tells us that, since 2 is less than 4, we can just write down that 2 to the left of the other numbers (2103) and know we're done. Sure enough, 147 in base 4 is 2103!

TIP #2: If the given number is less than the square of the base to which you're converting, you can do everything in a single step. All you have to do is work out the quotient and the remainder, write the quotient to the left of the reminder, and you're done! For example, what is 59 in base 8? 59 ÷ 8 = 7 remainder 3. Write down the 3 as before. Thanks to tip #1, we know that we can write the quotient down to the left, since 7 is less than 8, so we just write the 7 down next to it!

For base 8, this will work for any number less than 8 × 8, or 64. Similarly, for base 5, this will work for any number less than 25 (5 × 5), and so on. 44 in base 7? 44 ÷ 7 = 6 remainder 2, so we can quickly give the answer as 62!

Being able to convert to base 2 and base 8 in your head can be a great asset when working with computers. Practice this skill and have fun with it. You'll not only have a useful skill, but something with which to amaze and amuse others, as well!

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How To Instantly Convert Weeks to Minutes

Published on Sunday, September 21, 2014 in , , ,

Tfa1964's photo of the Zimmer tower at Lier, BelgiumA little over a year ago, I teased Grey Matters readers with a mystery skill. First, they had to learn to easily multiply by 63, then learn how to easily multiply by 72. The skill itself was revealed to be how to roughly convert any whole number of years into seconds!

In this post, you'll learn a similar skill: how to convert weeks into minutes instantly!

Back in the days before computers and calculators, this was a popular feat among entertainers who performed as human calculators. It was quick and direct to perform, yet was highly impressive to audiences.

One week has 7 days, and each day has 24 hours. Every hour, of course, has 60 minutes, so if we multiply out 1 week × 7 days/week × 24 hours/day × 60 minutes/hour, we get 10,080 minutes in a week. The number 10,080, as it happens is very easy to multiply by almost any number of weeks. If you keep the number of weeks at or below 124 (about 2.37 years), the numbers are even easier to work out.

STEP 1: Ask for any number of weeks less than 2 years (104 weeks). As an initial example, we'll say an audience member gave the number 36.

STEP 2: Write down the number they just gave you. In our example, you'd write 36.

STEP 3: Multiply this number by 8 in your head, and write this result to the immediate right of the first number you wrote. This is simpler than it sounds; all you have to do is double the number 3 times. For 36, doubling once gives you 72, doubling a second time gives you 144, and doubling a third times gives you 288. Writing 288 next to the 36 you wrote earlier gives you 36288.

NOTE: In step 3, it's very important to always treat the answer as a 3-digit number. For weeks from 13 to 104, it will be, but for weeks from 2 to 12, it will be a 2-digit number. You can change this into a 3-digit number simply by adding a 0 to the left of it. If you're given 7 weeks in step 1, you write down the 7 as in step 2, then multiply 7 × 8 to get 56, which becomes 056. You would write 056 as your step 3 answer, giving 7056, and then continue with step 4.

STEP 4: Write a zero to the immediate right of the other numbers, add commas where appropriate, and you're done! In our example, we add the zero to the right, giving us 362880. With commas, that result is 362,880. This means that there are 362,880 minutes in 36 weeks!

With a little practice, you'll be astounded as to how quickly you can pick this impressive skill up. You can quiz yourself by having Wolfram|Alpha give you a random number of weeks from 2 to 104, and then use it to verify whether you've worked out the correct answer.

HANDY BONUS TIP: You can make this more impressive for an audience by having someone with a calculator verify this in a long, drawn-out manner. Tell them to put in the number of weeks given, then multiply by 7 for the number of days in a week, then multiply by 24 hours in a day, and then multiply by 60 minutes in a week. Multiplying it out the long way makes this feat seem more difficult, as you're hiding the simple 10,080 conversion factor.

Try it out and amaze your friends!

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Days and Knights

Published on Sunday, September 14, 2014 in , , , ,

Mbdortmund's chess knight photo with DafneCholet's Calendar* photoAs you can probably tell from this recent post and this recent post, I've spent quite a bit of time thinking about the Knight's Tour lately.

These thoughts have reminded of a different type of Knight's Tour puzzle. This unusual variation involves moving the knight around a calendar.

It was 4 years ago, during September or October, that I was looking for blog post inspirations and ran across a thread on the XKCD forums, titled “Knight's Tour revamped”, which suggested playing the Knight's Tour on a calendar.

There was an added challenge, however: With your starting square being considered as move #1, how many dates could you land on that were the same as the move number? For example, if move #1 started on the 1st of the month, both the move number and the date would be 1.

As you can see in the original thread, the original poster used a July 2010 calendar and managed to find a complete Knight's Tour on which the 2nd, 6th, 11th, and 23rd moves landed on the dates of the 2nd, 6th, 11th, and 23rd respectively. Not surprisingly, it was Jaap of Jaap's Puzzle Page who found an 8-match solution.

I filed this in the back of my mind, but never really did anything until I ran across the Solving the Knight’s Tour on and off the Chess Board post which I mentioned last week. I liked the basic idea of being able to input a shape, and have the computer work out the tour, and especially the idea of using it to work out the XKCD forum's calendar challenge.

With a little knowledge of Java and graph theory under my belt, I managed to work out a program to solve it. For my fellow Java programmers, here's the main portion of my program, and here's the KnightsTour class I wrote to support it. Most of the hard work is done by lines 590 to 749. Those and lines 20 to 23 can removed if you're interested more in the general Knight's Tour than the particulars of the calendar challenge.

One of the first things I did, not surprisingly, was to find out how many day-to-move matches I could find in this month's calendar. I also found 8, all of which are highlighted below in red:



Yes, I've gone through every possible calendar, starting on every possible date, and learned quite a few interesting things in the process:

• Due to the fact that the number of days in a week (7) is odd, and the fact that the knight always moves an odd number of spaces (3), this means that a Knight on a calendar will always move from an odd date to an even date, and vice versa (just like what your teacher taught you about adding even and odd numbers). This, in turn, means that it's impossible to get ANY date matches if move #1 begins on an even-numbered date, as all the odd moves will land on even dates, and vice-versa.

• The above fact also means that if you start on an even date in a month with an odd number of days (29 or 31), you won't be able to complete a Knight's Tour.

• Yes, Jaap's 8-match path is the best one possible for July 2010 in particular. It also happens to be the only way to get 8 date-to-move matches in a Knight's Tour of a 31-day month beginning on a Thursday.

• Given any random month and year, you can always find a complete Knight's Tour and at least 6 date-to-move matches. Surprisingly, these minimum matches aren't found in the shortest months, as you may expect. With 30- and 31-day months starting on a Saturday, as well as 31-day months beginning on a Friday, 6 is the highest number of date-to-move matches you'll be able to find.

• There are months with 9 date-to-move matches, but none with more than that. 9 date-to-move matches can be found in a 29-, 30-, or 31-day month starting on a Tuesday or a Wednesday. In a 29-day month starting on a Thursday, or a 31-day month starting on a Monday, you can also find 9 date-to-move matches. You can often find more than 1 way to get to these matches, as well.

As it happens, next month (October 2014) is a 31-day month starting on a Wednesday, and here's one of the 3 possible ways to get 9 date-to-move matches:



I chose this one simply for the elegance of the column containing 16-23-30 and the diagonal containing 12-20-28. I also find it interesting that so many powers of 2 have date-to-move matches (2-4-8-16).

For the more math-inclined geeks, I'll wind this post up with all the maximum number of matches I've found, including the dates on which they start:

28-day months, starting on:
Sunday:    7 matches, beginning from the 1st or 23rd
Monday:    7 matches, beginning from the 1st or 21st
Tuesday:   8 matches, beginning from the 25th
Wedneday:  8 matches, beginning from the 1st
Thursday:  8 matches, beginning from the 1st or 5th
Friday:    8 matches, beginning from the 1st or 15th
Saturday:  7 matches, beginning from the 23rd or 25th

29-day months, starting on:
Sunday:    7 matches, beginning from the 1st
Monday:    7 matches, beginning from the 1st or 27th
Tuesday:   9 matches, beginning from the 25th
Wedneday:  9 matches, beginning from the 1st or 11th
Thursday:  9 matches, beginning from the 1st
Friday:    7 matches, beginning from the 1st, 5th, 27th, or 29th
Saturday:  7 matches, beginning from the 1st

30-day months, starting on:
Sunday:    7 matches, beginning from the 7th or 23rd
Monday:    8 matches, beginning from the 27th
Tuesday:   9 matches, beginning from the 25th
Wedneday:  9 matches, beginning from the 11th
Thursday:  8 matches, beginning from the 1st
Friday:    7 matches, beginning from the 1st or 7th
Saturday:  6 matches, beginning from the 1st or 25th

31-day months, starting on:
Sunday:    8 matches, beginning from the 23rd
Monday:    9 matches, beginning from the 7th or 31st
Tuesday:   9 matches, beginning from the 1st, 23rd, or 25th
Wedneday:  9 matches, beginning from the 7th
Thursday:  8 matches, beginning from the 5th
Friday:    6 matches, beginning from the 1st, 5th, 7th, or 31st
Saturday:  6 matches, beginning from the 1st, 23rd, 29th, or 31st

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More Quick Snippets

Published on Sunday, September 07, 2014 in , , , , , , , ,

Luc Viatour's plasma lamp pictureSince I've changed my posting schedule, I seem to have neglected my monthly snippet posts!

Not to worry, however, as we're kicking off September with a good round-up of different takes on some of my favorite mental feats.

• One of the longest-standing tutorials on Grey Matters is the classic Knight's Tour. The traditional version usually happens on an 8 by 8 chessboard. What about other irregular, non-rectangular shapes?

Over at the Wolfram Blog, Jon McLoone explored that question using Mathematica in his post Solving the Knight’s Tour on and off the Chess Board. If you're interested in the programming and the math, there's plenty in this article. Even if you don't care for all the math and programming, the variety of boards with successful Knight's Tours is amazing and amusing. Who knew Pac-Man could play the Knight's Tour so well?

• Over in the Mental Gym, I have a full tutorial on squaring 2-digit numbers in your head. I've often wanted to move on to squaring 3-digit numbers, but never really found a method that suited me. However, I recently ran across a video tutorial from Mind Math called Mental Math Trick to Square 3-digit Numbers for Faster Calculation. It breaks the problem up into 2 steps, working with the hundreds digit followed by the remaining 2 digits as a group. If you're used to squaring 2-digit numbers, this method isn't difficult to learn and adapt:



• Back in March, I wrote a post about calculating powers of e in your head. At the time, I was unaware of Colin Beveridge's post, Secrets of the Mathematical Ninja: Estimating Powers of e, which featured a quicker, yet less accurate estimate.

After seeing my post, Colin took it upon himself to develop an improved method, which he posted as Powers of e Revisited: Secrets of the Mathematical Ninja. When you're done exploring those posts, check out the rest of Colin's Blog!

• Another favorite blog topic of mine is calendars. Beyond the standard day of the week for any date feat, there's plenty of interesting mathematical patterns and shortcuts waiting to be discovered in the calendar. One of the best round-ups I've found on the internet is P.K. Srinivasan's Number Fun with A Calendar (PDF version). Besides the PDF version, there's a zipped .DOC version and even a video demonstration of some of the topics from the book:



That's all for this month. I hope you found these enjoyable and useful!

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Review: The Knight's Tour: A Scenic Journey

Published on Sunday, August 31, 2014 in , , , ,

Mbdortmund's chess knight photoOne of my favorite mental challenges, as many regular Grey Matters readers know, is the Knight's Tour. The challenge is, using only the chess knight's L-shaped move, to land on each of the 64 squares once.

Mentalist Richard Paddon recently released a download resource titled The Knight's Tour: A Scenic Journey. In this post, I'll take a close look at this new take on a classic feat.

We'll start with a quick peek at Richard Paddon himself performing the Knight's Tour, via the teaser ad:



The Knight's Tour: A Scenic Journey comes as a set of 3 files: A 45-page PDF of the same title, a 16-minute MPEG file of Paddon's performance, and the Knight's Tour Windows application used by Paddon, and programmed by Dave Everett.

In the PDF, right away, the author emphasizes the importance of developing drama in the Knight's Tour presentation. The first parts of the actual instruction, however, focus on developing the path through the board. Much of this part of the book may be familiar to readers of the “Knight's Tour” section of Paul Brook's Chrysalis Of A Polymath. However, Richard Paddon does add some new and helpful notes, such as the section on what he has dubbed “delta values”, which are familiar to those who have programmed a Knight's Tour, but little discussed in the use of performances.

In the next half of the book, Paddon discusses the presentational details. He starts with the benefits of the Knight's Tour, including its uncommon nature, and its huge potential on an emotional and theatrical scale. The thoughts behind the presentations are well laid out. Even if you disagree with any aspect of the presentation as written, you at least have a good starting point of why particular choices were made.

One of the more interesting choices is ending on a selected square, as seen in the above video. As the board empties, the chosen square becomes a more and more important focus, and becomes a natural point of building tension. The PDF winds up with a detailed description of how to use the program.

There are very few weaknesses in this product overall. One of the one that stands out to me as both a programmer and a blogger of mental feats was the choice of the Comic Sans font for the numbering of the board. If you're taking as much care as this author does to make an impact on the audience, there's probably better ways to label your board than a font designed specifically to have a comic-book appearance. On an equally minor note, the lightning in many of the shots of the performance video could be better. The importance of the video is for a more complete understanding of the presentation, so this isn't a huge drawback.

Overall, this is an excellent value for anyone seriously interested in performing the Knight's Tour. The basics of working through the path may be easily accessed in multiple sources, but the depth of knowledge that is presented, as well as the use of multiple media to demonstrate this make this the most complete lessons about all aspects of the Knight's Tour and its proper performance.

It's available for only $9.95 over at Lybrary.com and is a remarkably great value for that money. If the Knight's Tour interests you, Richard Paddon's The Knight's Tour: A Scenic Journey is a must-read.