Used to be able to perform basic calculator functions when entering numbers in the distance mate field.  I upgraded to 2015 SP4 and can no longer do this.  Simple example, I have a beam flange that is 7.995" wide, need to center a plate 5.5" wide on the beam flange.  Click mate, select dimension (auto-filled at 1.000"), enter 7.995-5.5, hit enter and it reverts back to 1.000".  In previous versions, I could enter 7.995-5.5, hit enter, and have it display the answer highlighted as the new value in the field (2.495), press right arrow to remove the highlight of the value, press /2 to divide the value by 2, and it would return an answer of 1.2475, select mate entities and hit ok.

Basically it worked exactly like the built in calculation functions that are still available in the dimension dialog box.