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Once the user has made a selection of astronomical observations of interest, the appropriate calibration observations can be found by means of the CALSELECT command. This command makes use of the Observation Type code, to find observations of a specified type within a specified number of days before and after the selected observations of the input table. The syntax is:
Valid keywords are DAY_LIMITS, WINDOW and OBS_TYPE; the keywords DAY_LIMITS and WINDOW are specific to CALSELECT only. DAY_LIMITS, specifies the time window in days to be searched around the date of each observation, while WINDOW specifies the maximum number of calibrations to be selected with each observation, according to:
DAY=(n,m), where n and m are the number of days before, and after, or
DAY=n , where n is a window in days, centred on the date of observation.
Similar use of WINDOW applies: WINDOW=(n,m) or WINDOW=n.
The default for DAY_LIMITS=(7,7); the default for WINDOW=(10,10). The default selection of the observation type code OBS_TYPE, is > 10, which indicates calibration observations. In practise it is often better to search more specifically for selected calibrations, and override the defaults by explicitly specifying the keywords.
If the input table for the CALSELECT command contains more than 100 entries ARCQUERY will prompt the user to confirm the action. The execution of this command can involve a lot of table handling operations and sorting, and therefore may take some time to complete.