  Arrangement theory plays an essential role in the study of the unfolding
model used in many fields. This paper describes how arrangement theory can be
usefully employed in solving the problems of counting (i) the number of
admissible rankings in an unfolding model and (ii) the number of ranking
patterns generated by unfolding models. The paper is mostly expository but also
contains some new results such as simple upper and lower bounds for the number
of ranking patterns in the unidimensional case.
