Monthly report for March 1999 by Christian A. Hummel: Together with Hutter, Mozurkewich, and Elias, Hummel conducted and reduced astrometric observations including the artificial introduction of siderostat pivot offsets which were used to compare delay line and siderostat metrology. These test helped uncover a mistake in the calculation of the constant term metrology corrections. Hummel and Elias found close correlation on short timescales of siderostat environmental temperature variations and delay changes, reinforcing the need to include a model of these effects in the astrometry data reduction. Hummel continued to work on the IDL version of OYSTER, the 6-way beam combination code of CONSTRICTOR, and scheduling and data reduction of more than 16 nights of NPOI observations.