Magnetic vector directions have been measured at 119 points over the field of a large, long-lived sunspot on 1966 September 19, when the spot was closely at central meridian passage. Further developments in Treanor's method of determining field directions enable the directions to be obtained independently for the violet and red sigma-components in the Zeeman patterns of the absorption lines. Reliability of the determinations is indicated by agreement between these two results, and for such agreeing determinations the field configuration shows a simple axially symmetric arrangement which is also supported by the field strength measurements. A discussion of the accuracy obtainable in field direction measurements, by Treanor's and by other methods, shows the greater potentiality of Treanor's procedure. The discussion leads also to the conclusion that apparent anomalies in the present results, at least in the sunspot umbra, lie within the uncertainty of the observations. For some of the penumbral regions, however, the apparent inconsistencies in the deduced magnetic field directions may indicate a genuine solar effect.