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C. A. Hummel (USNO)
One of the original design goals for the Navy Prototype Optical Interferometer is wide angle astrometry, which is based on the observation of the stellar fringe delay. We discuss recent progress in correcting this delay for atmospheric refractive index fluctuations, and explain in detail the algorithms used. This correction is one of three, the other two being due to motions of the siderostat pivot and changes in the feed system path length. The latter two are monitored with a laser metrology system and observations of an internal white light source. We summarize the current status of astrometry with NPOI.