Hello David Brown! The answers you seek will take a bit of explaining along with good drawings, some formulas and accurate definitions. Follow this up with action model testing and very careful measuring (to make several points). For starters, on the bench, extreme accuracy is not required in measuring off the six lever arms, but reasonably good accuracy is required. Knowing where and why to measure the arms at particular points is another thing. The line of compliance (so called Magic Line) is overrated as a critical item. Nice to have it if possible (usually close anyway, if not right on, in many cases), but secondary to emphasis on the lever arms, action ratio and weight / inertia issues. I started a paper on this and hope to complete it before the Mayan calendar runs out. I will be giving a class on exactly these items at WestPac III in Phoenix next March 2013; perhaps you can make it. In the meantime, if you require this information soon, please call me (you have my cell #) and be prepared to spend some time on the phone and have a pencil and pad handy. I expect others may want to get the ball rolling at this point. Regards Nick <div class="gmail_quote">On Wed, Sep 19, 2012 at 3:59 PM, Brown, David <<a href="mailto:dcbrown@mail.smu.edu" target="_blank">dcbrown@mail.smu.edu</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">All - Asked this question on the wrong list………. I have enjoyed very much the ratio discussions, especially the ongoing one as few weeks ago ( key in , key out etc) that Nick and several others contributed to. My question- What is a practical way to actually take those measurements, especially the key measurements? Many times I will put a long center pin in a wip flange, tie off some carpet thread and use that to look at the lines of compliance for key- wip- capstan, but how to measure key in- key out accurately and predictably? Calipers? Rulers? Also, I have seen a couple of ways to measure for key in - from balance point to the end of the keytop, from balance point to where the front pin enters the key. This relates some to what Fred was posting, but thought another topic would not muddy things up. Thanks for this interesting discussion David David C. Brown RPT Piano Technician Division of Music Meadows School of the Arts Southern Methodist University Dallas Texas <a href="tel:1-214-768-3976" value="+12147683976">1-214-768-3976</a> <a href="mailto:dcbrown@smu.edu">dcbrown@smu.edu</a> [cid:244020A4-F74B-47C9-84DB-458AE37E6657] </blockquote></div> -- Nick Gravagne, RPT AST Mechanical Engineering