Degrees ↔ radians.
Converts degrees ↔ radians. π radians = 180 degrees.
Radians are natural units for calculus and trigonometry; degrees dominate everyday and engineering use.
Most programming languages' built-in math functions (sin, cos, tan) expect radians, not degrees, which is a common source of bugs for anyone coding trigonometry without converting first.
180° = π radians ≈ 3.141593 rad.
Calculus, physics, and any equations involving derivatives of trig functions — the math is cleaner in radians.
A less-common unit where 400 gradians = 360°. Used in surveying in some countries.
It traces back to ancient Babylonian base-60 mathematics and astronomy — 360 divides evenly by many numbers, which made it practical for calculations long before calculators existed.