5100 and 5105 chairs include free float lockable tilt function with adjustable weight counterbalance. 5115 and 5115HR chairs include button operated synchronised seat and back tilt with adjustable weight counterbalance, and click back height adjustment.5100 and 5105 chairs include free float lockable tilt function with adjustable weight counterbalance. 5115 and 5115HR chairs include button operated synchronised seat and back tilt with adjustable weight counterbalance, and click back height adjustment.5100 and 5105 chairs include free float lockable tilt function with adjustable weight counterbalance. 5115 and 5115HR chairs include button operated synchronised seat and back tilt with adjustable weight counterbalance, and click back height adjustment.5100 and 5105 chairs include free float lockable tilt function with adjustable weight counterbalance. 5115 and 5115HR chairs include button operated synchronised seat and back tilt with adjustable weight counterbalance, and click back height adjustment.