Lyman 438 scope

I recently got one of these scopes and need to know how to "lock in" the eye relief. Do you just tighten up on the screw below the front ring, or do you also tighten the screw to the side of the rear (adjusting) ring? Any help would be greatly appreciated. This is my first scope with external adjustments.
Pete

"Be kind to your neighbor, he knows where you live"