An important point is that XAssist works with a ``caching'' mentality, which means that (most of the time), if a file exists that it needs to create, it will skip that step. Conversely, if you want a step to be repeated (i.e., if XAssist is updated or you change your mind about some setup), then you should delete the relevant files first.
After installing xassist (see above), create a directory where you want the processing to take place. When XAssist is run, it will create a directory for each field you want to process (although it currently can only work with one field at a time so it must be rerun for each field). It currently doesn't have the field lookup capabilities that are in qlook, but qlook can be used first to get the list of fields.
Invocation is as follows:
xassist (-r) (rootname fldname)
if -r is given, xassist proceeds as far as it can and then quits non-interactively (i.e., good for batch processing).
rootname is a string that will be the prefix of most of the files created by XAssist, usually the best choise is simply a short name for target of interest in that field (e.g., n3998). fldname is the name of the field to be processed. ``xassist -r n0193 rh702767n00" will download and process the ROSAT HRI data for field rh702767n00. Or if you just run ``xassist'' (or ``xassist n0193 rh702767n00``) you can use (hopefully intuitive) menu options for setting preferences and stepping through the processing interactively.
There is a shell script ``xassist_test'' which will download Chandra ACIS data for NGC 4203 and run xassist. Run this script to test your installation and to see xassist run (this will create several directories and files within the directory where you run it so you may want to run it in an empty directory). Below is a step-by-step example for running xassist manually.