For 1990-2009 cars

You cannot perform a proper wheel alignment on an alignment rack that is no longer level or is out of calibration. Check the alignment rack for levelness and calibration at least once a month. In order to get an accurate caster reading and establish standing curb height, the turnplates or the slider plates must move freely. Take the turnplates or slider plates apart at least once a year in order to clean and lubricate. Replace badly worn turnplates.