  We show that high-resolution observations of resolved Zeeman split lines can
be used to obtain new constraints on the stellar magnetic field geometry. In
particular, the contrast of the field strength distribution over the stellar
surface can be deduced from the differential measurement of the second moment
of the pi and sigma Zeeman components. Our analysis of the triplet lines in
slowly rotating cool magnetic CP stars uncovers a surprisingly homogeneous
field structure, inconsistent with any low-order multipolar geometry.
