The measure of an angle is the amount of rotations required to get to the terminal side from the initial side. A common measure of an angle is derived by placing its vertex at the center of a circle of some fixed radius.
            There are two commonly used measurements for angles: Degrees and Radians

Sexagesimal System: (Degree, Minute and Second)

            If the initial ray rotates in anti-clockwise direction in such a way that it coincides with itself, the angle then formed is said to be of 360 degrees ().
            One rotation (anti-clockwise) =
             rotation (anti-clockwise) =  is called a straight angle
             rotation (anti-clockwise) =  is called a right angle.

1 degree () is divided into  minutes () and 1 minute () is divided into  seconds (). As this system of measurement of angles owes its origin to the English and because,  and multiplies of  and , so it is know as English system or Sexagesimal system.

            Thus  rotation (anti-clockwise)                       =         
            One degree ()                                              =         
            One minute ()                                               =         

Conversion from  to a decimal form and vice versa.
(i)          =    
(ii)         =    

Example:         Convert  to decimal form.

Solution:           and
                       
                                               

Example:         Convert  to the  form

Solution:                    
                                               
and                                
                                               
Therefore,
                               
                                               
                                               
                                               
                                                 rounded off to nearest second
            Thus