Off Topic: Error in Table Of Powers Of Two

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John Mann

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Oct 9, 2025, 3:22:34 AM (yesterday) Oct 9
to [PiDP-1]
Hi,

I noticed in the "PDP-1 Handbook" Copyright 1960, 1961, 1962, 1963
that there is an error on page 72.

Zooming in on the values for 2^30 and 2^31
---
  1 073 741 824     30     ...
  2 147 483 848     31     ...
---
we can see that the 3rd-last digit of 2^31 should be a "6" not an "8",

===
So, I wondered where else this error appeared ...

It is there in the previous edition "PDP-1 Handbook" Copyright 1960, 1961, 1962
page 64

And F-45P1 PDP-4 Programming Manual
page A-22

And "The digital Small Computer Handbook 1970 Edition" Copyright 1967, 1969
- manual for for PDP-8's

===
In other DEC documentation it is correct 

F-55 2/84 PDP-5 Handbook
page 69

DEC-10-NRZC-D decsystem-10 Assembly Language Handbook, third edition Copyright ... 1973

 http://www.bitsavers.org/pdf/dec/pdp10/TOPS10/1973_Assembly_Language_Handbook/01_1973AsmRef_SysRef.pdf

page 194


DEC-10-XSRMA-A-D decsystem10 System Reference Manual, 3rd edition

  https://wwcm.synology.me/pdf/DEC-10-XSRMA-A-D%20DECsystem10%20System%20Reference%20Manual.pdf

page A-23



======


One _really_ strange thing I found is if you Google for wrong values 2147483848 or 2147483847
that apart from finding wrong values, you also get hits on PDFs containing the _correct_ value.
This includes having the wrong value in the "preview snippet" but the correct value in the PDF.

For example:
page 50
--- screenshot
Screenshot 2025-10-09 at 16.53.15.png
---
Chrome will find "84" only on the 1st line (3rd and 2nd last digits), and "64" only on the 2nd line. 
Same as when viewed in Preview, or in Safari.
Also, a text copy-and paste copies the *wrong* value, e.g.
--- text copy

♦define EqmInt-MIN -2147483848 ∕* From file limit∙.h : */

♦define EqmInt-MAX 2147483647

---

Not of much importance, but I found it interesting.

Thanks for reading this far,
    John Mann

Norbert Landsteiner

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7:26 AM (4 hours ago) 7:26 AM
to [PiDP-1]
As we're at it, there's also an error in the skip group (I think, this concerns all editions of the Handbook):


                                  SKIP GROUP

INSTRUCTION   CODE #              EXPLANATION                 OPER. TIME (µsec)

    szf       6400f      Skip on ZERO flag (f … flag #)              5
    ...
    szs       6400s0     Skip on ZERO sense switch (s … sense #)     5


As the observant reader may have noticed, there's a zero missing in the instruction code for "szf", `6400f`.
We may also observe that "szs" encodes the switch number in the second to last triplet (octal digit), which may already tell us where the zero is missing, as in `64000f`.

So, this should be:

                                  SKIP GROUP

INSTRUCTION   CODE #              EXPLANATION                 OPER. TIME (µsec)

    szf       64000f     Skip on ZERO flag (f … flag #)              5
    ...
    szs       6400s0     Skip on ZERO sense switch (s … sense #)     5



Best,
Norbert
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