2.1.992 Part 4 Section 3.17.7.150, IMARGUMENT
a. The standard does not fully specify how the angle θ is calculated.
Office calculates angle θ as ATAN2(x,y).
b. The standard does not specify how function arguments map to formula variables.
Office maps x + yi to argument complex number, and theta to ATAN2(x,y).
c. The standard states that the complex number can be in the form x+yi.
Office accepts complex numbers in the form x+yi and x+yj.