Superscript size percentage

Thanks for joining into this discussion. I am always interested in the origin of things; the back story; the history of the development of typesetting. Ratios of size proportions keeps showing up as I further my own knowledge of this partly-current / partly-ancient craft.

Mike, your point (pun intended) of 58.3% is the percentage of 7/12 is where the answer seems to be. Points and picas were the more commonly used typographic unit of measurement, and makes perfect sense to have a superscript/subscript ratio based on this system.

From the SDK: At least in the world-ready header comments these values are documented as defaults, there’s also a small cap scale factor of 0.7 dating back to version 3 aka CS (there as fixed rather than float) and versions in between.

I also skimmed thru several books from the 90s but found no explanation. Knuth mentioned using other values.

I’ve been meaning to ask this question for 26+ years: 

Hi ​@Mike Witherell , I can only guess, but I’m assuming this is a relic from Postscript Type 1 fonts which could not include expert sets like true small caps, superscript, subscript, etc in a single font file. Now any decent Opentype text font should have built in true superscript numbers, which you access at via Character > Open Type > Superscript/Superior (not Character > Superscript).

Where the superscript baseline should be is up to the font designer, so if there is no true superscript built in, I would think the preferences default is based on the default Minion’s x-height?

Here is Minion vs Emigre’s Vista which has an extra tall x-height. You can see the true superscript characters have a matching weight and are proportional to the lowercase characters. The fake Vista superscript sits too low because of its big x height, while fake Minion is just about right:

Interestingly, 58.3% is a ratio of 7/12 on the character size scaling factor. The position is up 33%, or 4/12. That adds up to 11/12 the scale of the text size.

Still wondering how ancient this calculation might be. One internet bot says this was the way QXP did it.