Paul Kustaanheimo was a member of a group of mathematicians based at Helsinki, who were all interested in some form of finite geometry. The most prominent members were G. Järnefelt, P. Kustaanheimo, and R.  Lehti. The origin of their inspiration is to be found in the work of J.T. Hjelmslev who developed so-called “natural” geometry (“Die natürliche Geometrie”, see his 1923 book), also referred to sometimes as “physical” geometry. Their approach has not known any continuation, one exception being Reisler and Smith (1969). However, in a strange way there is a connection with Suppes’ approach to be discussed later in the sense that geometry is primarily seen as (almost) an experimental science, i.e., the geometer deals with rulers and compasses, creates flat surfaces to measure, and so on. Of course, since we humans can only manipulate finite objects in finite ways, a discrete geometry must result.