  We deal with integrals of invariant measures of pairs of planes in euclidean
space $\mathbb{E}^3$ as considered by Hug and Schneider. In this paper we
express some of these integrals in terms of functions of the visual angle of a
convex set. As a consequence of our results we evaluate the deficit in a
Crofton-type inequality due to Blashcke.

Differential Geometry