The reference angle is the positive acute angle that can represent an angle of any measure. Reference point point of reference reference noun an indicator that orients you generally. In this web site points are shown either as a black dot or with a somewhat larger orange halo.
Its a quicker way maybe to solve for the inflection point h k and a.
The usual convention is to choose the reference point at infinity. The reference angle is the positive acute angle that can represent an angle of any measure. Even references and citations are a snap. Cube Cone Sphere Pyramid etc.