At the simplist level, the user plans their observing file in the following way:
Another point to consider is that all observers plan their observations based on a desired time range. Invariably, the actual time range assigned by the observing schedule will be different. The observing script that the user writes should be flexible enough to handle this situation. The use of relative times provides the user with a powerful and easy way to control the flow of their script without necessarily knowing the absolute stopping time of their project. Where the user should take additional care in preparing their scripts is to insure that observations do not begin too early. This is done both by specifying (in the comment section at the top of the script) the acceptable LST time ranges of the project and by specifying an absolute start time (the start keyword) to the first scan or loop commands. This is illustrated in each of the examples that follow.
The only drawback to using the start keyword is that the script will just wait around for the start time to be reached if the command is executed too early. Perhaps a better approach might be to observe calibrator setups until the specified start time is reached. For example, if the user did not want to begin the main loop until at least 15:00 LST and had a single calibrator with the setup name 3c273, the command
loop calsetup=3c273 stop=1500placed before the main loop would insure that the main loop would not be started until at least 15:00 LST and would observe (repetitively) the calibrator until that time. If this example command was called and the time was beyond 15:00 LST, it would be ignored.