The Speedmaster was the first watch to feature a tachymeter on the bezel as opposed to being incorporated into the dial. This opened up the dial, allowing for a better visual balance
link between the indices (which are fashioned from white gold on the
link Racing Master Chronometer) and the seconds track, but it
link also gave the tachymeter more room to breathe. Decoupling the tachymeter from the rest of the bezel ultimately made the watch more legible, and in turn, easier to use.