The Horton Machine toolset has gained a certain stability during the years, and I currently use it in my Hydrology class. There is a tutorial in Italian and an out-of-date Reference Manual which are waiting for being merged into a unique English Manual. Meanwhile, here it is a paper that explains it, as much as it can be made in a paper. This would be part, after having passed the appropriate peer review, of an open access book of the British Society for Geomorphology, Clarke (2013), section 2.4
The book chapter draft can be found here. The complimentary material to reproduce the manuscript figures can be found in this post.
Clarke, L.E. (Ed.) Geomorphological Techniques (Online Edition). British Society for Geomorphology, London. ISSN: 2047-0371,