The secret lies within the angles. As is demonstrated in the image below, each digit included originally a corresponding number of angels.
Bonus Fact 1: The digits we use today in the western world are commonly called ‘Arabic Numbers’, but actually they were developed in India. Moreover, they are not in use in Arab countries, but rather another version of them – the ‘Eastern Arabic Numbers’.
Bonus fact 2: the Roman numerical system had no digit for zero, and it was expressed in the absence of any marking.
Bonus fact 3: The numeral system we use today was developed in India in the 6th century. The Arabs adopted it in the 9th century, following a book published by the mathematician Muhammad Ibn Musa Al-Khuwarizmi. Later, the Jewish scholar named Abraham Ibn Ezra, followed by the Italian genius Fibonacci, introduced the method to Europe, where it was quickly adopted as a substitute for the Roman system and implemented both in commerce and science.