dimension "linked value" value

I have a part that I did not create. It is a simple weldment, straight line, with short, equal, colinear reference lines at each end. A structural member is created at the line. We have taken over the sketch to change things parametrically. The o.d. and wall thickness, also have values that are linked to some other value. When I double click on the dimension to get to the modify box, I have the option to unlink the value, but no way to determine what the value is linked to. How do I determine what the linked value is?

Thanks,

Mike Lydon

SolidworksSketching