Insert a new Rebar and link a Mark to it. Edit the Mark data and generate the BBS as shown in the previous section.
Insert a standard AutoCAD linear dimension (either the _DIMLINEAR or the _DIMALIGNED commands will do). The length pointed by this dimension is going to serve as the input value for the Range paramenter in our Mark.
Double click the Mark to edit it and click the button to pick the dimension; the Mark now shows the field [E = …] linked to the dimension. Click OK to close the form. From now on this dimension will be dynamically linked to the Mark and provide the value for the Range parameter. Any change to the dimension will affect the liked Mark as well.
Stretch the dimension and verify that the number of bars displayed by the Mark is modified accordingly.