This must be done if you wish to calibrate the polarization of your data, but should also be done for phase-referenced data. In the latter case this is necessary to remove the geometrical phase due to the different positions on the sky of the target and phase reference source. The pipeline places this (since Jan 2003) in CL2.
>TASK 'CLCOR'
>OPCOD 'PANG'
>CLCORPRM 1,0
>GO