GNU Emacs Calc 2.02 Manual
7.4.2 Polar Mode
The Calculator normally "prefers" rectangular complex numbers in the
sense that rectangular form is used when the proper form can not be
decided from the input. This might happen by multiplying a rectangular
number by a polar one, by taking the square root of a negative real
number, or by entering ( 2 SPC 3 ).
The m p (
calc-polar-mode) command toggles complex-number
preference between rectangular and polar forms. In polar mode, all
of the above example situations would produce polar complex numbers.