It had to do with the use of the hyphen on a typewriter keyboard. Two hyphens without a space constituted a dash, but something to do with spaces and whether a range was indicated such as within a group of numbers.  I have some old typewriter training books somewhere. My memory banks from classes 50 years ago have only vague recollections.  I'll find it, I thought maybe someone here might know.

I've found them.  One is from Gregg's Typing Manual from the 40's, and the other is Rowe's College Typing from the late 50's.  Two hyphens with no space in the sentence, and no space between them is a "formal dash".   I guess that would be your em dash.  ex.: "Honest, industry, tact--these are qualities that win success."

An "informal" dash is a hyphen with a space before and after.  ex. "Three phases of activity - production, distribution, and accounting - are the basic factors in most in most types of business."

A short dash is used to designate "to".  It is a single hyphen with no space before or after, thus:  "Pull from the shelf the items with part numbers A1832-A1855."

Then of course the hyphen used what it is normally used for,  such as in a hyphenated word.


 

M. Höhne wrote:

Interesting. In the typewriter world, this kinda makes sense because you have to convey two or three ideas with only one printing character. That "formal dash" is what I'm used to and it serves as an em dash, as you note. That "informal dash", though, seems to serve the same purpose---and why? ---a double dash is too "formal" for some purposes? Can't see it, myself; might be some other reason. If I wanted to make an em dash on a typewriter, I would move the platen down a half-line-space and type an underscore---sort of a superscripted underscore (which would, of course, end up about mid-line).

That "short dash" being used to function as an en dash---that just doesn't work. Your part number example could just as clearly (typographically) be a single eleven-character part number.

Still, I didn't work in business in those days and maybe they made it work. That's what standards and conventions are for, after all.

Today I use that informal dash in telephone numbers just because it's easier to read. Now I have a name for it.

Thanks for this interesting bit of history.

You are so right about the part numbers!  Let's not forget the dash number in  O ring sizes as well.  But a I get the point.  Business correspondence and convention for writing on a machine had  to, on some level, come into it's own--as well as borrowing from the typographer's world.