The PSS (Point Source Searching) program was written for use in the ROSAT project, originally on WFC data. The anticipated nature of the data from the WFC drove the decision to separate the determination of the background (which was expected to contain large gradients) from the detection of the sources (which were expected to be almost exclusively unresolved). This separation is somewhat artificial, as the determination of an accurate background often involves detection of sources, which in turn needs a background. However, the methods of producing backgrounds depend greatly on the nature of the observed objects. While a local background estimation may be sufficient for flat backgrounds containing few point sources, the method will break down when presented with extended sources superimposed on a galaxy cluster emission containing large spatial gradients. The atomic nature of ASTERIX applications enables backgrounds to be derived or fitted in a number of ways by combining simple programs.