The GRIP project has provided partial support for UNC's advanced technology tracker work and is a customer for trackers designed by this team. As noted last year, the UNC optical tracker is attractive in the PIT because it is immune to the electrical noise created by the motors in the PHANToM. This electrical noise causes significant error in our current commercial magnetic trackers. The new lightweight optical tracker was deployed early in the reporting period and has undergone testing, calibration and algorithmic refinement during this reporting period with RMS noise of 0.1 mm in position and 0.03 degrees in orientation. The system measures position and orientation in a 26 by 30 foot working area and makes 1500 to 2000 measurements per second with less than 1 millisecond of latency. Software has been developed and tested for multiple simultaneous trackers operating under the same ceiling (n = 2 currently) to support deployment of this tracker in the PIT. Experiments were conducted to determine an optimal pattern of tracker ceiling tiles (the tracker's LED beacon system is located in the tiles) for the PIT two-user configuration. We expect to deploy the tracker over the PIT before the end of March 1998.