Monthly report for March 1998 by Christian A. Hummel:

CAH observed a change in position angle and separation for the newly
discovered binary Zeta Orionis.

CAH demonstrated that correcting the NPOI delay measurements with the
white light observations decreases systematic errors in the former and
enhances the visibility of FK5 positional errors in the NPOI data.
A star position fit significantly reduces the residual delay errors.