To calibrate the EVN antennas you need the final version of the antab file, which will be provided by JIVE. This file contains the gain curves for each antenna (in K/Jy) as well as system temperature measurements (in K) taken during the course of the observation.
The OFFSET parameter is useful in the cases where the data do not contain continuous . In this case the measurements usually lie at the beginning and/or at the end of the scans, but not within! OFFSET lengthens the scan by a user-specified amount, allowing AIPS to include the measurements.