The 40Ar/39Ar dating technique has become one of the most widely used methods in the field of isotope geochronology today. However, the increasing number of ages generated by the 40Ar/39Ar dating technique, more and more requires a consistency in the complex calculation of these ages and their errors. ArArCALC (http://earthref.org/tools/ararcalc.htm; Koppers, 2002) has been designed to calculate 40Ar/39Ar ages within a single software program starting with basic noble gas mass spectrometry data and ending with the simul-taneous calculation and display of plateau, total fusion and isochron ages. It has been widely used by re-searchers and students both in the United States and in international laboratories since its online publication in 2001. This award will expand and update the ArArCALC Freeware package to add new "Advanced Data Reduction" capabilities that will be of great benefit to most 40Ar/39Ar geochronologists today. Three sepa-rate updates are proposed over a two year period, in particular, to ensure complete error propagation throughout all the age calculation algorithms, to add new visualization tools allowing users to better study their dating results, to provide a complete user-guide in PDF and HTML that fully describes the functional-ity, algorithms and program philosophy, and finally to ensure easy transfer of the age dating results into the Radio-Isotope Geochronology (RiG) databases that are currently being developed under http://earthref.org and CHRONOS. The impact of these software updates extends well beyond the benefits to the 40Ar/39Ar geochronologists alone. The easy dissemination of 40Ar/39Ar age dating results, stored in single ArArCALC data files, allows for an increased and straightforward exchange of age calculation results between different researchers, between different laboratories, and between principal investigators, their students and scientists outside 40Ar/39Ar geochronology. The fact that all calculation parameters are stored in each ArArCALC age calculation file and that they can be viewed - and edited - at all times, makes this software an excellent tool for teaching undergraduate and graduate students the intrinsic details of 40Ar/39Ar geochronology.
