If you look at a wide range of modern clocks, from the cheapest on the market to some luxury options, a huge proportion of them have numbers that look the same.
They are typically made up of a set of seven different glowing elongated hexagonal shapes, which can be used to display every number easily, as well as most letters of the alphabet.
This is known as a seven-segment display, so named for the idea that you can display every single number and every letter with just seven segments, three horizontal and four vertical in two rows.
The initial idea of displaying numbers in seven segments actually pre-dates the LED technology that makes digital watches possible, during a time when watches that displayed the time as a number as opposed to a conventional dial used rotating disks and dials, similar to those formerly used in train stations.
Whilst there were seven-segment displays that used traditional filament bulbs, they were so huge that they tended to be only used as part of huge signal panels, such as for telephone operators or power plants.
What changed was the development of the light-emitting diode (LED), which allowed for tiny lights that used so little power they could feasibly be used as watches, albeit ones that you needed to press a button on to display the time.
Hamilton was the first company to make a digital watch, the Pulsar, in 1972. Inspired by the prototype work the company did for the film 2001: A Space Odyssey to create a watch of the future, the Pulsar was exceptionally simple and sleek.
By the next year, however, Seiko had found a way to make a watch with a liquid-crystal display, which allowed it to show the time permanently, and from there digital watches and clocks have only evolved further.