## Solidus vs division slash and fraction slash

I'm designing my first typeface and I'm at the point now where I'm working on punctuation, math symbols, etc. The not-so-major stuff that's actually kinda major in making a proper functional font. The face is an early 20th century flared serif. It's very close stylistically to ITC Symbol Black and I noticed in researching Symbol as well as other faces in the same vein that there is a difference between the solidus glyphs and the mathematical slashes. It looks to me like many of these fonts are using generic math symbols that don't match the design of the rest of the font. Maybe I'm overthinking but is there some kind standard when it comes to math symbols like the division slash, or is it fine to use the same glyph for the solidus and the math slashes?

Not to put to big a point on it, but how many mathematical users will select something like ITC Symbol Black to do any work? My guess is the number will approach zero...

However, think about it. The mathematical slash is used in an equation with other symbols, esp. if you're setting an equation in line, such a

[(1+1) + (17/2)] / (2x2) = 2.625

The spacing and shape of all the operators should harmonize. Some will set the equation without spaces around the operator, some with space, and in some cases, that will be the full word space, thought a thin space would be preferable.* Your sidebearings need to accommodate all of these, as best possible.

Secondly, if you're using lining figures, there is no reason for the slash to go below the baseline (though it should balance with parens & brackets). On the other hand, your solidus will go with letters that have a descender, so you can consider using one that dips below the baseline.

Etc. Etc. Form & function may be crippled in these modern times, but aren't quite dead yet, esp. amongst the people who actually use type. Consider what they need when they use it.

*Actually, it isn't all that uncommon these days to find the space character in a font real close to a 5-to-em space, around 200 units. And that's what Unicode calls a "thin space" (U+2009). If you're going to use such a small word space, 200 to 220 on a 1000 unit em, your thin and hair spaces should be appropriately smaller.** I use to use a 167/1000 for a thin (6-to-em) and 55/1000 for a hair, but sometimes have to rethink this, depending on the space value. & thinking on it, a 6-to-em is already in Unicode at 2006, but IIRC, not quickly addressable via InDesign.

** Or not. Old Linotype linecaster operators used "thin space" to mean an unexpanded spaceband wedge, so there is some precedent for setting it to the word space. But only as the smallest word space to be used. If you think of the normal 80%-100%-whatever that pops up in InDesign's justification panel, a thin would then be 160 with a 200 word space. Personally, I don't like this way of approaching a thin, but it is a personal decision.

This is definitely a display face I'm working on so I'm sure the mathematical glyphs won't be used often, but I've got a bit of a completionist streak in me so I want to make sure all of the basics are covered. I will probably ignore anything past the commonly-used glyphs (plus, minus, multiply, divide, etc). Your comment regarding the differences in baseline made a lot of sense so I think I will do the two different slashes, it's not like they are complex glyphs.

Thanks for the insight on spacing, too!