A method includes measuring a first thickness at a first location of the polishing pad and a second thickness at a second location of the polishing pad; obtaining a first reference thickness at the first location of the polishing pad, wherein the first reference thickness is an average thickness of multiple thicknesses at the first location; obtaining a second reference thickness at the second location of the polishing pad, wherein the second reference thickness is an average thickness of multiple thicknesses at the second location; calculating a first thickness difference; calculating a second thickness difference; modifying a conditioning parameter value at the first location of the polishing pad; and sweeping a conditioner across a surface of the polishing pad; and applying a downforce or a sweeping speed to the conditioner that urges the conditioner against the first location of the polishing pad according to the modified conditioning parameter value.