| [ | Date | | | 2025-03-31 23:42 -0400 | ] |
A recent article Yes, in the 1980s we downloaded games from the radio sparked discussion on how some users of home computers at the time routinely typed programs from print magazines, since access to the Internet was not practical, and bundled floppies were either not provided or often arrived damaged.
Without being eagle-eyed or an expert programmer, this is an error-prone process: more often than not, on its first run, the program would be incorrect, and debugging it would be difficult in the absence of either a large enough display or helpful error messages. One commenter mentions that some magazines started providing a checksumming program, that would let the reader verify that each of their lines of code matched the printed checksum.
I remember this being a feature built into the HP 32S II calculator. From its manual1:
Verifying Equations
When you’re viewing an equation — not while you’re typing an equation — you can press [↱][SHOW] to show you two things about the equation: the equation’s checksum and its length. Hold the [SHOW] key to keep the values in the display.
The checksum is a four-digit hexadecimal value that uniquely identifies this equation. No other equation will have this value. If you enter the equation incorrectly, it will not have this checksum. The length is the number of bytes of calculator memory used by the equation.
(I am taking the affirmation that no two programs share a checksum as a simplification meant to make the material easier to the reader.)
And, indeed, sample programs provided further down include checksums:
(As a side note, the program size is 28 bytes and a half: we can tell that this is a 4-bit machine.)
HP 32SII RPN Scientific Calculator Owner’s Manual, Edition 5, Hewlett Packard. The PDF copy I used says “File name 32sii-Manual-E-0424” and "Printed Date: 2003/4/24.↩︎
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David Haguenauer
<www@kurokatta.org>
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