In 2013 I wrote an article on the history of visual confusion between the shapes of the numeral zero and the letters 'O' and 'o', a perennial problem in monospaced computer fonts. Historically, though, the problem goes way back before the inventions of computers, typewriting, and typography. It has influenced the development of typographic numerals, and, in recent times, stimulated a wide variety of solutions in computer typography, as the article explains.

The essay was first published as "Oh, oh, zero!" in TUGboat: The Communications of the TeX Users Group, Vol. 34, No. 2, pp. 168-181, 2013 (http://tug.org/TUGboat/tb34-2/tb107bigelow-zero.pdf) and later was published in French translation by Jacques André as "Histoires d'O, d'o, et de 0" in Cahiers GUTenberg, No. 57. (http://bigelowandholmes.typepad.com/bigelow-holmes/2014/07/history-of-o-o-and-zero.html).

There have been many different design solutions to the problem, but, as my original article explains and illustrates, the methods have varied and there is no single, standard solution to the problem.

The TUGboat article elicited a letter from my former Stanford colleague, computer scientist Donald Knuth, inventor of the TeX system for mathematical and scientific publishing, and the Metafont system for type design. He expanded our understanding of the early history of the problem in computing, and described his favored method for distinguishing zero and capital 'O' - to make the 'O' squarish. (http: //tug.org/TUGboat/tb34-2/tb111knut-zero.pdf).

Professor Knuth ended his letter with a request that Bigelow & Holmes implement a similar solution in Lucida Console. And so we did, also in Lucida Grande Mono, by making the capital letter 'O' superelliptical.

The development of the "DK" (designed for Donald Knuth) versions of the fonts proved to be more complicated than estimated, involving more design history and a smattering of mathematics, so I have written about it as a third installment to the series. "About the DK versions of Lucida" can be found at (http://tug.org/TUGboat/tb36-3/tb114bigelow.pdf).

More samples of the resulting fonts can be seen at (https://tug.org/store/lucida/opentype-dk.html).

You might think that two articles and a letter is way more more than enough information on the subject, but the articles have prompted colleagues to send me yet more information, unintentionally omitted from either article. Jacques André reminded me of a 1968 article by H. W. Mergler and P.M. Vargo about using superellipses for computer drawn letter shapes, as part of an early, ambitious study of computers and letter design, long before Ikarus, PostScript, Metafont, TrueType and other digital font software developed in the 1970s and 1980s.

(https://s3-us-west-2.amazonaws.com/visiblelanguage/pdf/V2N4_1968_E.pdf)

Also, Erich Alb reminded me of Adrian Frutiger's solution to the zero/O problem in the OCR-B monospaced font design, based on Univers. Frutiger's solution is the opposite of Knuth's: in OCR-B, the capital 'O' is elliptical and the zero is squarish/superelliptical. As explained in my original article, those who propose solutions to the zero/O problem fall into two main camps: those who modify the zero and keep the more classical 'O' shape, whom I call the "humanists", versus those who modify the 'O' and keep the traditional zero shape, whom I call the "engineers". It seems that people prefer to preserve the character shape that is more important to them, and modify the one that is less important. Letters versus numbers. Although one of Frutiger's many accomplishments in typography is the use of numerical designations of type weights and styles, such as "Univers 55", his solution in OCR-B puts him in the "humanist" camp.