The formula of a real calculus is not allowed to refer to a complex number. Thus if you want to use the modulus of a complex number you have first to create a modulus of complex
You can then refer to this calculus (which is a real calculus) in another real calculus.
Here is an example :
Let's assume you have measured the affix of a point M in a frame (O;I,J) and named this affix aff.
You want to create a circle radius of which will be the half of the modulus of this affix.
You have to use icon of the calculations expandable bar (third from the bottom).
A dialog box pops up.
Select the affix aff.
In the edit field Name of the calculus, enter a.
Click OK.
When you will create the circle you will enter in the radius fields the formula a/2.