On the center of Watts' datum for the lunar marginal zone

Correction of a previous determination (Mulholland, 1977) of the three-dimensional location of the center of Watts' datum for lunar-limb corrections, removing a contamination from the FK4 equinox error, results in a longitude component x sub 2 of -1.08 + or - 0.5 km (-0.58 + or - 0.27 arcsec), which is in good agreement with Morrison and Appleby's (1981) recent determination. It is noted that the latitude component x sub 3 is irrecoverable and that the radial component x sub 1 is unaffected by the error. Therefore, the revised selenocentric vector of the Watts center is x = (+6.9, -1.08,...) + or - (2,4,0.5,...) km.