Talk:Pitch (typewriter)

Equivalent point sizes

"Everybody knows" that 10-pitch Pica is 12-point. But I can't see how that could be right. According to Point (typography), "In digital type, letters of a font are designed around an imaginary space called an em square. When a point size of a font is specified, the font is scaled so that its em square has a side length of that particular length in points." (It goes on to say that things are a bit more complicated but it is probably good for a first order approximation.) The Pica font is monospaced, so a 12-point font should have 6 em-spaces per inch. Which means the pitch is six? Or conversely, a 10-pitch font has 7.2 em-squares per inch. What am I missing? --John Maynard Friedman (talk) 22:13, 9 July 2021 (UTC)

According to IBM, "All fonts are measured in points, the vertical size of the font. [...] Point size is a baseline-to-baseline measurement, which includes minimal white space." So it may be that I'm confusing my horizontals [the basis of pitch] with my verticals [the basis of points]. But Pica and 'Elite' have the same vertical height, which suggests they should be the same point size? Do they have the same em-square? (the Pica em is wider that the Elite em, but same height). Still trying to find my blind spot. --John Maynard Friedman (talk) 23:51, 9 July 2021 (UTC)

As I have been unable to find a citation for this statement Expressed in point (typography) (and computing) notation, Pica is a 12‑point font and Elite is a ten‑point font, I have deleted it. Of course it can be reinstated if a reliable source is found. It is too significant an assertion in a very short article to be let stand. --John Maynard Friedman (talk) 17:57, 14 July 2021 (UTC)

Yes, "point size" is a vertical distance that varies from one font to another.

The traditional point-size names article mentions that "Pica" is a common name for fonts with a point size of 12 points high.

In traditional typesetting, a particular font was made up of a collection of sort (typesetting). The "point size" of that font is the physical height from the top surface to the bottom surface of that piece of metal, which is the same for each and every sort from that font, and is usually the distance from the top of the highest ascender to the bottom of the lowest descender.

Thin strips of lead go between one line of text and the next -- the leading.

"Everyone knows" that the IBM Selectric typewriter always shifted the paper up 1/6 of an inch on each carriage return (but, like you, I'm finding it difficult to find a reliable source for this). (For now I'm calling this distance "lines per inch vertically". Is there a better name ?). That distance is *not* the "point size", but (in typesetting terms) the sum of the "point size" plus the "leading".

The IBM Selectric typewriter#Type elements and fonts section says

"The font size was measured not in points but in pitch; that is, the number of letters per one inch of the typed line. As a result, 12-pitch fonts (12 letters per inch) were actually smaller than 10-pitch fonts (10 letters per inch), and roughly corresponded to the 10pt and 12pt traditional typographic font sizes."

and also mentions several "Elite" fonts in the "Small (12-pitch) fonts" list, and several "Pica" fonts in the "Large (10-pitch) fonts" list.

Those Pica and Elite fonts do *not* have the same point size -- they do *not* have the same vertical height from the top of the highest ascender to the bottom of the lowest descender.

Those Pica and Elite fonts, like *every* font for the IBM Selectric, have the same 6 lines per inch of vertical height -- the same 1/6 inch from baseline of one line of text, including the "normal" amount of leading (not the minimal amount), to the baseline of the next line of text.

Every font for the IBM Selectric is designed for either 10 characters per inch horizontally, or 12 characters per inch horizontally.

So apparently the IBM Selectric typewriter "Pica" fonts are, from the top of the tallest ascender to the bottom of the lowest descender, roughly 12 points high (with a tiny amount of leading, less than 1 point, to bring the total lines per inch vertically to 1/6 inch), and "Elite" fonts are roughly 10 points high (with somewhat more leading, about 2 points, to bring the total lines per inch vertically up to 1/6 inch).

So apparently those "Pica" fonts have a larger m-square, and those "Elite" fonts have a smaller m-square.

Does that answer your questions?

--DavidCary (talk) 22:17, 20 October 2021 (UTC)

Yes, that helps: almost. An Elite em at 12 ems per horizontal inch was 10 points tall and a Pica em at 10 ems per inch was 12 points tall, making each 'em-space' roughly square. There are 72 points in a vertical inch so six lines per inch implies 12 points per line. Which would imply no room for leading with Pica fonts... ?? --John Maynard Friedman (talk) 22:45, 20 October 2021 (UTC)

I wonder if I'm still making a math error... Elite is 12 em-squares per horizontal inch, making each em-square 1⁄12" or 6⁄72" wide. Being square, it is thus the same height – which implies 6 points high. Which is definitely wrong. Brain melt. --John Maynard Friedman (talk) 23:33, 20 October 2021 (UTC)

The point size of a font, and the size of its em-square, is entirely about the height of the font, and has nothing to do with the width. A "12 point font" is 12 points tall, and its em-square is 12 points high and (because it's square) 12 points wide, no matter what the width of any particular letter.

Yes, Elite on a typewriter is 12 characters per horizontal inch, which says nothing about the size of its em-square. Elite is also about 10 points tall, making each em-square about 10⁄72" high, and, since it's square, 10⁄72" wide.

Yes, Pica on a typewriter is 10 characters per horizontal inch, which says nothing about the size of its em-square. Pica is also about 12 points tall, making each em-square about 12⁄72" high or 1⁄6" high, and, since it's square, 1⁄6" wide.

As described in Dash#Approximating the em dash with two or three hyphens, the "em dash" is often approximated on a typewriter by typing two consecutive dashes. The total width of the resulting double-wide dash (when the typewriter is in the "12 character per inch" setting) is about 1/6 inch. Since all the printable symbols on a typical typewriter (including a single dash) have to fit in a box of the same width, all those symbols fit in a non-square box roughly twice as tall as it is wide.

All letters on a (typical monospaced) typewriter, including the capital "M" and capital "W", are roughly half the width of the em-square.

(Unlike typical typewriters), in normal (proportional) typography, the capital letter "M" is often the full width of the em-square (hence the name), and "W" is even wider.

(Like typical typewriters), in normal (proportional) typography, most letters are much narrower than the em-square.

--DavidCary (talk) 10:20, 30 October 2021 (UTC)

Your all those symbols fit in a non-square box roughly twice as tall as it is wide is precisely the source of my logic error. My premise was that a capital M almost fills a square (with a minimal spacing so that MMMMMMM is not an impenetrable black stripe). Is that ratio documented anywhere? (Yes, I know, the people who developed typewriters were rubbish at documentation, unlike nowadays. :-^ ) --John Maynard Friedman (talk) 14:17, 30 October 2021 (UTC)

References

vertical distances

When I pull the carriage-return lever of a typewriter, what is the name for the vertical distance typewriter pushes up the paper in preparation for the next line of text?

I see that the leading article calls this "the distance from one baseline to the next", and implies this is the sum of the "point size" plus the "leading".

For now I'm calling this distance "lines per inch vertically".

What are the typical "lines per inch vertically" distances?

"Everyone knows" that the IBM Selectric typewriter always shifted the paper up 1/6 of an inch on each carriage return. Did IBM invent the "6 lines per inch vertically" standard, or where did this come from?

The green bar paper section of the "Line printer" article briefly mentions both 6 lines per inch vertically and 8 lines per inch vertically, alas without any references at all in that section. (Where did the "8 lines per inch vertically" standard come from? Are there other standard "lines per inch vertically" distances for other typewriters or printers?). Alas, the lines per inch article seems to cover halftone graphical lines, not lines of text.

I see that RFC 678 calls this distance "characters per inch vertically". Alas, characters per inch redirects to this "Pitch (typewriter)" article, which seems to focus only on horizontal distances.

Is there some other article that covers vertical distances, and in particular what I've been calling "lines per inch vertically", or should this article be expanded to also cover vertical distance?

--DavidCary (talk) 22:17, 20 October 2021 (UTC)