Akinori Machino, writing for Medium, digs into the details of the San Francisco font. There are just a ton of fascinating details here. Just one tiny example:

[In other fonts], a colon will be placed right above the baseline, so it’s not vertically centered if it is placed between numbers. San Francisco fonts, on the other hand, will make it vertically centered automatically.

Great stuff. Apple’s constant attention to tiny details continues to amaze me.