Dr. Jaks “Behind My Blackboard”

[Tom Frame]

I’m reading The Book Test Book by Jim Kleefeld. One of the items is Dr. Jaks’ “Behind My Blackboard” that was published in The Gen in May 1959. It’s an intriguing, seemingly free number force. I’ve been obsessing about the powerful potential of this method for a week and I can’t unravel why it sometimes works and why it sometimes doesn’t work.

Persia Diaconis isn’t answering my pleading, daily, hourly calls, so I’m sharing the conundrum with you to see if we can crack the code.

You must perform the effect with a married person.

Print these questions on a piece of paper:

Year of your birth. ______

How many years you’ve been married. ______

Your age. ______

The year of your marriage. ______



Total: ______



According to Jaks, the resultant forced number should be twice the value of the current year. Kleefeld even describes the method using the year 2021. Thus, the force number should be 4042.

On page 40 of a book, you’ve previously memorized the second word on the fourth line. You can force the participant to choose that book from among several books, or just use one book.

While you avert your gaze, the participant writes her numbers on the paper, adds them on her wretched device and writes the total – 4042.

She opens the book to page 40, counts to the fourth line and remembers the second word.

You divine her word without asking any questions. That’s a strong effect!


Here is my data:

1960
20
61
2001
_____
4042

It works.


Here is my wife’s data:

1961
20
59
2001
____

4041

Off by one.


We tried this with my wife’s mother’s data and got 4040. Off by two.

Despite Jaks’ and Kleefeld’s claims, the force doesn’t work. Why do my numbers force 4042, while my wife’s numbers force 4041 and her mother’s numbers force 4040? And why are the deviations from the force number so small?

Does anyone understand the mathematical mechanics of this force and why it kinda sorta works?

[Richard Hatch]

Sure, it will work for the current year when both your birthday and anniversary have passed, since birth year plus age then equals current year and years married plus year married then equal the current year. Apparently you and your wife got married before January 21st and your birthday was also earlier this month, but hers hasn't happened yet. Your mother hasn't yet celebrated her birthday or her anniversay. December 31st is the only date this is sure to work, but the odds are good for dates well before that.

[Richard Hatch]

PS: So the range of answers will always be 2xcurrent year, or 2xcurrent year minus 1 (as for your wife) or 2xcurrent year minus 2 (in the case of your mother). In the case of this year, 4042, 4041 and 4040. Easy enough to remember the 2nd and 1st words on line 4 of page 40, you just need to give them a word in the case where the last digit is zero, as for your mother. How about having them look at the last word on the line in that case?

[Dave Le Fevre]

Richard has summed it up perfectly.

When I read the algorithm, I realised that many people would get discrepancies of 1 or 2. We married in 1976, it's now 2021, hence 45 years.

However, our wedding anniversary this year hasn't yet happened, hence 44 years. Hence a discrepancy of 1.

And the same discrepancy for birthdays - my 2021 birthday hasn't happened yet.

The later in the year that one uses the proposed method, the higher the probability that it'll yield the required result. An excellent method at xmas.

And conversely. And it's only January, therefore ...

[Tom Frame]

Ooooh, I get it. Very cool. Thanks Richard.

[Richard Hatch]

My anniversary is December 31st, so it only works exactly once a year for me!

[Tom Frame]

Richard,

Oh, but what a wonderful, magical moment that will be for you and your wife. Make the most of it!