I am trying to use my part's smart dimension's value as a global variable's value inside the equation manager with

"global_variable" = "D1@Sketch1"

But SolidWorks says "the syntax of this equation is incorrect". Can you use smart dimension values inside of equations?

This is a reduced version of my larger problem, which is to set a part's fillet radius equal to the radius of a circle inside of a sketch of a separate imported part. For this use I cannot use the standard technique of "global_variable" = 2cm then "fillet_radius" = "global_variable". Even if there is a better way to do this, I still want to know in general how to use smart dimension values in equations.

I'm on Windows 10, SolidWorks 2013 (upgrading to 2017 isn't a option)

EDIT: Even using

"global_variable" = 1
in the equation manager produces the message "the syntax of this equation is incorrect". Perhaps I have a much deeper problem going on.