The coordinate transformation is defined and performed by the SLALIB package of routines written by P.T.Wallace (see Starlink User Note 67). All the information required for the transformation from the (X,Y) coordinate system of the measurement to the (RA,DEC) system of the IAM file is held in the ASCII housekeeping file. The basic organisation of the information is carried out by the SCOSPOS library of routines, with support from the SPORTHK library for accessing the ASCII housekeeing files. All the routines are written in FORTRAN.