The first-order reversal curves (FORC) diagram method for the characterization of magnetic materials and of other materials showing hysteretic phenomena is gradually replacing the classical use of the major hysteresis loop or of other selection of magnetization curves. The FORC diagram offers to the experimentalist an image of the sample which can be related to the coercivity and interactions fields acting on the magnetic entities within the sample. Of course, this information should be analyzed carefully since errors in interpretation can be possible in the absence of other related physical or phenomenological models. However, in the wider use of the FORC diagram method there are a number of obstacles. One major problem is that the FORC distribution is not usually easily represented by analytical functions and due to that inconvenient are difficult to handle in Preisach-type simulations. Another solution would be to evaluate the geometric properties of the FORC distribution using statistical formulae applied directly to the experimental FORC. In our previous work [Tanasa et al., 2005], we have presented such a statistical approach of the experimental FORC diagram measured on the thermal hysteresis of spin-transition materials. In the full paper we are presenting in details a set of statistical parameters which can be used directly on experimental FORC distribution.