FWIW --- I will be teaching on these very concepts at the WestPac III Conference this coming March in Phoenix. Briefly, David is correct in that the proof must be in the pudding; i.e., theory and calculations should dovetail with real world events. Precise measurement of the components can be tricky, but the layout of true lever (aka moment) arms should follow standard engineering protocols. Laying out and measuring on the diagonal (conjugate arms) goes way back to the European (read German) system. Dr. Walter Pfeiffer was a leading proponent here but his reasoning had more to do with eliminating friction and gross mismanagement of parts layout than with insisting that his system of measuring the "arms" was the only way, or that, in fact, his lever arms were actually "moment arms". He says referring to his "lever arms" as shown in his drawings: "In the strictest sense, we would probably have to speak, not of a front and back lever arm of the key, but rather of the effective length of the front and back portions of the key lever. Accordingly, the same holds true for the terms upper and lower lever arm used for the whippen..." Dr. Pfeiffer clearly knows the difference between a true lever arm and an "effective" connection of the parts, the purpose of which is to control the component layout as to minimal friction and ease of rotation along the lines of gearing principles. This was a primary focus of his. NG <div class="gmail_quote">On Wed, Jan 16, 2013 at 8:17 PM, David Love <<a href="mailto:davidlovepianos@comcast.net" target="_blank">davidlovepianos@comcast.net</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> <div link="blue" vlink="purple" lang="EN-US"><div>I’m sure he has, and he’s not the only one. This topic came up not too long ago and several methods were outlined by various people. If you have keys made by various key makers around the country you will discover that the methods they use can yield quite different numbers which makes communication along these lines difficult at best. An action from one key maker I know targets something around 4.8 as his standard but that same action produced by another keymaker would be considered 5.6. Those differences are all owing to how they measure the individual levers. One of those two must be wrong, it seems to me, or at least have some other meaning. The discussion that came up previously was which method of measuring most closely mirrors the SWR method that comes about from an analysis by weight. I’m sure DS could chime in on that, if he wanted to. Finding a system in which weight and distance methods yield the same numbers under ordinary conditions seems like something important. So far, I find the system that I use (not the hammer travel/key travel number but the individual lever measurements, to be the most consistent in that respect, though it’s not perfect. David Love <a href="http://www.davidlovepianos.com" target="_blank">www.davidlovepianos.com</a> <div style="border:none;border-top:solid #b5c4df 1.0pt;padding:3.0pt 0in 0in 0in"> From: <a href="mailto:pianotech-bounces@ptg.org" target="_blank">pianotech-bounces@ptg.org</a> [mailto:<a href="mailto:pianotech-bounces@ptg.org" target="_blank">pianotech-bounces@ptg.org</a>] On Behalf Of Dale Erwin Sent: Wednesday, January 16, 2013 6:35 PM To: <a href="mailto:pianotech@ptg.org" target="_blank">pianotech@ptg.org</a><div class="im"> Subject: Re: [pianotech] Measuring Action Ratios</div> </div> Perhaps David Stanwood could weigh in on this. No doubt he's experienced this in his massive studies of such things. <div class="im"><div>Dale Erwin R.P.T. Erwin's Piano Restoration Inc. <tt> </tt> <tt></tt> </div><div><div><pre style="background:white"><tt> </tt></pre></div></div></div></div></div></blockquote></div> -- Nick Gravagne, RPT AST Mechanical Engineering