For Hoefler & Frere-Jones, it’s all about the sweating the small stuff. While developing Gotham, they noticed that the fractional one appeared naked and needed a serif. So, they decided to add it to all of the other fractions.
It’s something that we added because we felt it mattered. Even if it helped only a small number of designers solve a subtle and esoteric problem, we couldn’t rest knowing that an unsettling typographic moment might otherwise lie in wait. We’ve always believed that a good typeface is the product of thousands of decisions like these.
That’s called attention to detail.