IBM 1620 invalid character symbol

[Ken Whistler via Unicode]

Philippe,

Those aren't negative digits, per se. The usage in the manual is with an 
overline (or macron) to indicate the flag bit. It does occur over a 
zero, and in explanation in the text of floating point operations, it is 
also shown over letters (X, M, E) representing digits of the exponent 
and mantissa. See p. 27 (31 of the pdf) in that same manual, for an 
extensive discussion with lots of examples in the text:

http://www.bitsavers.org/pdf/ibm/1620/A26-5706-3_IBM_1620_CPU_Model_1_Jul65.pdf

The Unicode representation of the text material printed on that page 
would best be done with a combining macron, I think.

--Ken


On 9/26/2017 6:34 AM, Philippe Verdy via Unicode wrote:
> But what is interesting is the use of negative digits (-1 to -9, with 
> the minus sign above the digit; I've not seen a case of minus 0, not 
> needed apparently by the described operations)
> How do you encode these negative decimal digits in Unicode ? with a 
> macron diacritic ?
>

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