A classification of sundials

Summary The first attempt at a classification of sundials appeared only in 1953, in the catalogue established by Henri Michel for the Museum of Liège. It was immediately followed, in the same year, by the article by Kathleen Higgins, exclusively dedicated to this topic. The influence of this second study has spread out throughout the numerous articles on sundials that have been subsequently published. The aim of the present paper is to bring some order to these two old classifications, which are in fact quite similar and were sufficiently valid at the time, and to propose a new approach to the problem based, for the first time, on principles directly linked to astronomy and geometry. Moreover, this latter approach has the advantage of a flexibility in its application to all kinds of sundial collections.