Line linked to another?

[Julian Boot]

Hi,

Can someone suggest how I might make one line change size when  
another line is updated?

Eg,


Line 1:  o-----------------------o

Line 2:  |------- 100 mm --------|


When I move a end point of Line 1, I want Line 2 to remain parallel  
and change length.

Is this doable?

-Julian