## hpb file

However, the calibration is not done directly on the IPB files, which, in principle, are never updated offline. Instead, CLIC normally works on header files, or hpb files. Before one starts the calibration, the observation headers from the IPB file are copied into the hpb file, and calibration sections are added in the header for later use. The default is to add only the antenna calibration sections, because the instrumental calibrations are usually done per antenna and the baseline sections are much bigger in size. However, one can also create an hpb file with baseline sections if needed (see also table 2).

Besides the calibration sections, designed to store the amplitude/phase gain solutions as a function of time or frequency, two sections are mandatory in the hpb file: the data file section and the data modifier section. The data file section contains the name of the IPB file from which the data were copied and the index number of that observation in the IPB file. The data modifier section contain parameters which modify the data after they are read from the IPB file. This allows to correct the data for e.g. new baselines measurements (see section 4.7 for more details) without modifying the IPB file. This section also contains a flags structure similar to the one in the IPB file. CLIC considers the logical .or. of the two flags structure when an hpb file is opened.

After the calibration is complete, one just needs to save the hpb file (and the uv table for analysis) and the IPB file can be deleted. If there is a new need to redo part of the calibration or produce new uv tables one just has to download again the IPB file. Note that any access to the data requires the IPB file to be present on the file system in any of the IPB_DATA1: to IPB_DATA9 logical names containing directories.