This paper describes the architecture of an image and data level comparative visualization system and experiences using it to study computational fluid dynamics data and experimental wind tunnel data. We illustrate how the system can be used to compare data sets from different sources, data sets with different resolutions and data sets computed by using different mathematical models of fluid flow. We include recent improvements including use of the comparison of vector fields, ability to interactively interrogate the comparisons, addition of new metrics, the latest FEL2.0 and VisTech libraries, and GUI for a calculator module.