In the annulus method the background RA and DEC should be set to the same as that of the source box. To avoid including source photons in the background box the user is prompted for an inner and outer radius. The inner radius should be made slightly larger than the source box radius and the outer radius should be made as large as possible without including any other sources or overlapping a rib or the central ring structure. It is recommended that you use the procedure XRTBCKBOX to define a source and background box.