This report summarizes the work performed during the past two years at the National Institute of Standards and Technology (NIST) in the refinement and formal definition of the MESF unit of fluorescence intensity. In addition to the theory underlying the MESF unit, considerations of error analysis are also presented. The details of this work may be found in the three publications of the NIST Journal of Research (www.nist.gov
) listed as the references 2-4. The use of the fluorescence intensity unit provides a tool to compare quantitative fluorescence intensity measurements over time and across platforms.