There are three systems for the measurements of angles. That is,

(1) Sexagesimal system (unit is degree)

(2) Centesimal system (unit is grade)

(3) Radian or circular measure (unit is radian)

The comparisons between three systems are as follows:

Sexagesimal system: In this system, one right angle is equal to the 90 degrees (1 right angle $=90$ degrees), one degree is equal to 60 minutes (${1}^{\circ}=60$ minutes) and one minute is equal to the 60 seconds ($1\text{}minute=60\text{}seconds$).

Centesimal system: In this system, one right angle is equal to the 100 grades, one grade is equal to 100 minutes and one minute is equal to the 100.

Radian system! In this system, one right angle is equal to the 90 degrees ($1\text{right angle}=90\text{}degrees$), one degree is equal to $\frac{\pi}{18}0$, radians and one minute is equal to the 60 seconds ($1\text{}minute=60\text{}seconds$).

$\pi \text{radian}={180}^{\circ}={200}^{g}$

The circular system or radian system is more preferable, because it gives the equivalence relation between other two systems.