In a late 1980s trade journal, I saw a full-page of polar balance diagrams for each major engine type. For each engine type (V6, V8, inline 6, inline 4, V12, etc) a circular polar chart was presented with overlaid color-coded graphs showing 1st, 2nd and 3rd order balance for 360 degrees of crankshaft rotation. By "balance" I think it depicted inertial forces in the crankshaft rotational plane. E.g, an inline 6 had an almost circular graphs since it has almost perfect first and second order balance. By contrast an inline 4 had oblong graphs. I don't remember if engines assisted by balance shafts were shown. On that one page, you could easily see the engine smoothness of each type. Does anyone remember seeing that or have any idea what journal it was? Have you seen any similar graphic?