Wolfram Function Repository
Instantuse addon functions for the Wolfram Language
Function Repository Resource:
Compute the reference angle to a given input angle
ResourceFunction["ReferenceAngle"][θ] gives the reference angle to the angle θ. 
Compute a reference angle:
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Compute the reference angle for angles lying in each of the four quadrants:
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Plot the reference angle function for all angles between 0 and 2π:
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ReferenceAngle works directly on Quantity expressions with units of "Radians":
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ReferenceAngle will remain unevaluated for nonnumeric input:
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ReferenceAngle throws away the sign of its input:
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