Difference in the application of the full 4π beam model versus the pencil beam approximation. Panel A): difference between survey 1 and survey 2 for a 30 GHz radiometer (LFI-27S) with the 4π model, smoothed to 15°. We do not show the same difference with pencil beam approximation, because it would appear indistinguishable from the 4π map. Panel B): double difference between the 4π1-2 survey difference map in panel A and the pencil difference map (not shown here). This map shows what changes when one drops the pencil approximation and uses the full shape of the beam in the calibration. Panel C): zoom on the blue spot visible at the top of the map in panel A). Panel D): same zoom for the pencil approximation map. The comparison between panels C) and D) shows that the 4π calibration produces better results.