On the right hand side of my cross slide is a set of 4 screws which are locked in place with small nuts. These adjust the gib-strip which is a bar down the inside of the dovetails which hold the cross slide in place. By adjusting the screws you can ensure that the cross slide moves in a straight line without being too stiff. This arrangement is designed to compendate for any wear in the mechanism. You will find these adjustments on a wide range of equipment such as lathes, mills, grinding machinges, x-y tables and anything else that uses a dovetail slide.
In Model Engineer’s workshop No. 154 David Lewis suggests an interesting idea which is to put small ball bearings on the end of the screws to spread the load of the screw onto the gib-strip. I’ve not tried this but his collegue, a former Adcock & Shipley apprentice said it was the best modification that could be made to a slide.