Mind Hacks
by Tom Stafford & Matt Webb

The unconfirmed error reports are from readers.  They have not yet been 
approved or disproved by the author or editor and represent solely the
opinion of the reader.

Here's a key to the markup:
        [page-number]: serious technical mistake
        {page-number}: minor technical mistake
        <page-number>: important language/formatting problem
        (page-number): language change or minor formatting problem
        ?page-number?: reader question or request for clarification

This page was updated February 28, 2008.


UNCONFIRMED  errors and comments from readers: 



(xix) 4th paragraph;
The first sentence, "The information transforms in the brain are made yet more complicated by the constraints...." doesn't make sense.


{167}  3rd paragraph;
The method for calculating the century-item adjustment for Gregorian dates is
incorrect, since 5 mod 7 = 5, not 0.  If we had used the proposed method and
calculated 5 mod 7 correctly, then we would actually get:

20 / 4 = 5
5 mod 7 = 5
3 - 5 = -2
2 * -2 = -4?

Obviously this does not yield the result in Table 4-11, p. 166.  If we omit the
modulo operation and replace the division with a modulo 4 operation, then we do get
the results in Table 4-11:

1700s:
17 mod 4 = 1
3 - 1 = 2
2 * 2 = 4

1800s:
18 mod 4 = 2
3 - 2 = 1
2 * 1 = 2

1900s:
19 mod 4 = 3
3 - 3 = 0
2 * 0 = 0

2000s:
20 mod 4 = 0
3 - 0 = 3
2 * 3 = 6

2100s:
21 mod 4 = 1
3 - 1 = 2
2 * 2 = 4

2200s:
22 mod 4 = 2
3 - 2 = 1
2 * 1 = 2

2300s:
23 mod 4 = 3
3 - 3 = 0
2 * 0 = 0

In general, perhaps the author meant, "To get the century-item for any Gregorian
date, cast out fours, subtract the result from 3, and multiply the difference by 2."
Or, in rough mathematical terms:

2 * (3 - (C mod 4))
where C is the century, such that C = 20 for the year 2005.