HP 1055CMHP - Manual (Page 145)

Service Calibrations
5-29 HP DesignJets 1050C and 1055CM Printers Service Manual
8 Lower the Carriage Assembly slightly, by turning the T9 screw shown below
anti-clockwise and then check for a scraping sound again as shown previously
in step 7.
9 On moving the Carriage Assembly along the length of the printer you should
now hear a scraping sound: this sound indicates that you need to raise the
Carriage Assembly (if there is no sound repeat step 8).