Sutherland, W. R., On-Line Graphical Specification of Computer Procedures, M.I.T. Lincoln Lab., Tech. Report No. 405, Lexington, Mass. (May, 1966). It is available as Ph.D. at "http://theses.mit.edu". I downloaded it with wget as gif images through the "Overview of thumbnail pages" service. No need to buy it. Juhana -- http://music.columbia.edu/mailman/listinfo/linux-graphics-dev for developers of open source graphics software