π = 3.14
Angle 180° = π radians. Angle 360° = 2π radians.
Advantages of measuring in radians
In calculus and most other branches of mathematics beyond practical geometry, angles are universally measured in radians. This is because radians have a mathematical "naturalness" that leads to a more elegant formulation of a number of important results.
Wikipedia, Radian, 2019
π is strictly a property of circles and spheres. Angle 180° = 3.14 radians = 314 centiradians. Angle 360° = 6.28 radians = 628 centiradians.
π and 2π are 314 and 628 centiradians respectively. This was known recently, however this was portrayed in the Quran 1400 years before it was discovered.
[Quran 96:8] But to your Lord is the return.
"Al-Rujaa الرُّجْعَىٰ" means return to the same location. In this verse disbelievers can go in any direction but eventually they will come back to the same location. But this can only be true if Earth is spherical. You can only return to the same location if Earth is spherical. And if Earth is spherical then a full circle would make 2π rad.
π and 2π are 314 and 628 centiradians respectively. It turned-out that the gematrical value of the word "الرُّجْعَىٰ" is 314 and the gematrical value of this entire verse "إِنَّ إِلَىٰ رَبِّكَ الرُّجْعَىٰ" is 628. These are the same values of π and 2π in centiradians.
1400 years ago the letters "ي" and "ى" were written the same without any dots as "ى". The gematrical value of both is 10. The entire word "الرُّجْعَىٰ" has gematrical value of 10 + 70 + 3 + 200 + 30 + 1 = 314. The entire verse "إِنَّ إِلَىٰ رَبِّكَ الرُّجْعَىٰ" has a gematrical value of 628.
How could an illiterate man who lived 1400 years ago have known that whatever direction you go you eventually come back to the same location? How could he have known about a full circle in centiradians? How could he have known that Earth has properties of a sphere?