The first step is to gather the information that will be needed to plan a program and to reduce the data. Information that is more or less permanent is stored in several MIDAS table files:
All of the above information, except for program-star tables, should already be available to you. Only if you are the first user of PEPSYS at an observatory will you need to construct the Observatory and Horizon tables yourself. They are described in the Appendix; see also section 13.6.1 below. The Observatory file is very simple, and data for the Horizon file for a telescope can be collected in a few hours (the command MAKE/HORFORM will help you compile the horizon data). Program-star tables are described below, along with the MAKE/STARTABLE command provided to produce them.
In addition, you will need information about the instrument. As instruments tend to evolve with time, you will probably need to put this information together for each observing run separately. The MAKE/PHOTOMETER command will ask you questions, and make a new file from your answers; it can also show you the contents of an existing file. If an instrument is fairly stable, and a previous instrument-configuration file is available, you may be able to just edit the old file, using the EDIT/TABLE command.
Some of the instrumental information may not be available at the time you plan your observing run. You can give ``don't know'' responses to questions about such things, or leave items blank if you have no information. However, for the sake of accuracy, you should try to obtain as much of the missing information as you can before reducing the observations.