Refrencnce Button in constraint definition Window

[araminaran]

Hi Friends
I have a question. when we want to make a dimension between for example two points by using constrain option, there will open a constraint defition window (look at the attached picture). can anybody explain what does the reference button exactly do in this window?
thank you all

 

[MrCATIA]

The Reference option will turn the constraint into a non-driving dimension that does not effect the size of the sketch. (It's like a construction mode for constraints)

I use it as a measurement. For example if I have a right-triangle with the angle and acute side constrained making the sketch fully constrained. If I add constraints for the obtuse and hypotenuse lengths, the sketch is over-constrained, unless I make both of these reference constraints. Now, If I change the angle, I see the lengths of all sides.