The concept of the h-expression was introduced by Howard Eves as a generalization of various products of ratios of directed lengths that appear in important results of Euclidean geometry like Ceva's and Menelaus's theorems. On the other hand, h-expression is a generalization of the cross-ratio as a basic numeric invariant of projective geometry. The central topic of this paper is Eves's theorem which states that h-expression is a projective invariant. This theorem provides the possibility of a variety of applications, both in proving geometric theorems as well as in practical examples, such as a photogrammetry where the measurements in a two-dimensional image are used to reconstruct the relationships between sizes in the three-dimensional original. Furthermore, the basic properties and applications of another geometric invariant are presented. This geometric invariant is closely related to Eves's h-expression, but it refers only to the isomorphisms of projective configurations. Therefore, they are not necessarily induced by projective plane transformations. Nehring's sequences of points and lines are crucial in this approach. They can be associated with different configurations, and the corresponding h-expression remains constant with regard to variation of the choice of the starting point. Hence, it is an isomorphism invariant.