i only do this for ease but you should measure each distance of where the rack sits in relation to the outer body for true centre and then set the steering column/ wheel appropriately. Finally if on refitting your steering wheel is slightly out of centre just loosen the rack clamps and move it slightly sideways to micro correct. if it is further offset than a small amount then you will have fitted the splined drive of the steering column a little out, easier than you might think even when marked prior to separating it!
