IBM 1620 invalid character symbol

Ken Shirriff via Unicode unicode at
Wed Sep 27 13:10:33 CDT 2017

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.

I'm asking my sources to see if I can find out more about the 1620's
characters, but haven't come up with anything concrete yet.


On Wed, Sep 27, 2017 at 10:42 AM, Ken Whistler via Unicode <
unicode at> wrote:

> Asmus,
> On 9/27/2017 10:02 AM, Asmus Freytag via Unicode wrote:
> In that context it's worth remembering that there while you could say for
> most typewriters that "the typewriter is the font", there were noted
> exceptions. The IBM Selectric, for example, had exchangeable type balls
> which allowed both a font and / or encoding change. (Encoding understood
> here as association of character to key).
> That technology was then only two years in the future.
> And in some sense, not even... ;-)
> By the 1950's (and probably earlier), enterprising linguists and other
> special users were conspiring with skilled typewriter repair experts to
> customize their manual typewriter keyboards and key strikers with custom
> fonts. I have an example sitting in my office -- an old Olympia manual
> typewriter with custom-cast type replacing the standard punches on some of
> the key strikers, and with custom engraved key caps added to the keyboard,
> to add schwa, eng, open-o, etc. to the typewriter. It also has the bottom
> dot of the colon *filed off* to create a middle dot key. Typing an actual
> colon on that machine requires an "input method" consisting of 3 key
> presses: {period, backspace, middledot} A couple of the keys that have
> raised accents on them were modified so as disable the platen advance,
> thereby becoming permanent "dead keys" -- effectively emulating the
> encoding of combining marks. There are probably thousands of such
> customized manual typewriters still sitting around, over and beyond the
> various standard manufactured models.
> --Ken
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