SF Pro uses "optical sizes." The font automatically adjusts its tracking (spacing between letters) based on the point size. At smaller sizes (Text), the spacing is looser to prevent letters from blurring together; at larger sizes (Display), the spacing tightens for a cleaner look. High X-Height:

SF Pro belongs to the sans-serif tradition—the same lineage as Helvetica, Univers, and Arial. However, unlike the cold, mathematical uniformity of Helvetica, SF Pro incorporates subtle Humanist details that dramatically improve on-screen readability.

Whether you are an iOS developer, a UI/UX designer, or a typography enthusiast, understanding SF Pro Regular is essential for mastering modern digital design. The Origins of San Francisco

At the absolute center of this typographic system sits —the baseline weight engineered to solve the complex challenges of high-density screen readability, responsive scaling, and brand consistency. The Origins of San Francisco