This rule was originally designed by Sama Etani and manufactured by Concise. Model 600 is for chemical engineering and has Periodic Table of Elements on the back as well as the "Data Center" which is tacked in the pocket of the body. The Data Center contains a lot of tables such as the unit conversion, physical constants and others.

This particular version was specially manufactured in 2003, in memory of Mr. Michael O'Leary who was a great slide rule collector and owner of the International Slide Rule Group at Yahoo.