IBM 1620 invalid character symbol

[Ken Whistler via Unicode]

Ken,


On 9/27/2017 11:10 AM, Ken Shirriff via Unicode wrote:
> The IBM type catalog might be of interest. It describes in great 
> detail the character sets of the IBM typewriters and line printers and 
> the custom characters that can be ordered for printer chains and 
> Selectric type balls. Link: 
> http://bitsavers.org/pdf/ibm/serviceForConsultants/Service_For_Consultants_198312_Complete/15_Type_Catalog.pdf 
>
>

That is a very interesting source, though from a much later era (1983). 
In particular, the "Special Character Nomenclature" (p. 11 of the pdf) 
provides a good list of what the IBM typographers at the time thought 
was the range of special symbols they were working within this overall 
collection.

Note the presence of the group mark, the record mark, and the segment 
mark. And in the realm of potential "tofu" indicators, there is the open 
box and the OCR blob, but nothing like the 1620 symbol(s) we've been 
talking about.

On another point, the "pillow" noted for the invalid character in the 
IBM 1620-2 (using the Selectric instead of the older IBM typewriter 
model) was almost certainly also not an actual punch on the Selectric 
type ball, but instead implemented by an overstrike of "[" and "]". See, 
e.g., the Pica 72 type style in the catalog noted above, which looks 
like some of the very earliest Selectric type. Its use could well have 
been occasioned by the fact that the slab serif typewriter font would 
have created a muddy blob if you tried to overstrike an "X" and and "I" 
for this output symbol.

--Ken