50g

Why HP 50g uses this definition of principal value of ARG(z) of a
complex number z: (ARG(z=x+y*i)-> ATAN(y/x)+(1-x/ABS(x))*pi/2?

-pi<principal value of ARG(z)<=pi ->
http://en.wikipedia.org/wiki/Complex_number#Polar_form

Ex. ARG(-1-1*i)=(5/4)*pi instead of -(3/4)*pi

Greetings,
Simone.