Hi there,
As itsmyjob has alread pointed out, there are COPY LENGTH
and COPY RADIUS for you to pick up when you're creating your line or circle respectively. While creating your line/circle, move your cursor to another line/circle, MB3+Parameters+Copy Length/Radius.
Or supposing you've already created a number of cirlces/lines, and you've also assigned a length/radius constraint to ONE of the line/circle. Then you may try Ctrl+C the contraints, next Ctrl+V on those lines/circles. As a result, those "slaves" will subsequently follow the value of the "master".
Of course, in all cases, no link!!
Cheers. Kennis.