Monthly report for April 2003 by Christian A. Hummel: Hummel implemented a new tool in OYSTER replacing the 7 orbital elements of a binary by the 5 elements of an apparent ellipse and orbital period and periastron epoch. The transition between them is provided by the Thiele-Innes constants. Hummel derived preliminary orbits for 27 Tau and 12 Boo from NPOI data. He communicated the results to D. Pourbaix and A. Boden, respectively. Hummel wrote both a writer and reader for NPOI data in the new FITS format adopted for optical interferometry data by the IAU working group. He used a library of basic FITS IO written in IDL by J. Monnier. Hummel implemented FDL limit checks in the scheduling software.