This is just a wild, hypothetical musing... but could the tight coil provide some minimal level of friction upon itself?  In other words, a loose coil is not contacting the winding above it, hence it does not have the associated friction to help keep it in place. <div>On 3/25/07, RicB <<a href="mailto:ricb@pianostemmer.no">ricb@pianostemmer.no</a>> wrote:<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> Interesting.  Don is one of those guys that pays attention to this kind of detail... so if he says he's measured and observed some small difference I certainly wont discount his claim out of hand. I dont see the mechanism that would achieve this tho... at least not clearly. Cheers RicB     I certainly would not let down the tension to tighten coils.     With respect, I have measured the difference in unison stability with     sloppy coils. There is a small but measureable difference, after lifting     coils and tapping them down to form nice tight coils on upright     pianos that     are 50 years old and equipped with humidity control systems.     I routinely check each new client's piano by testing three pins. If     there     is no pitch drop then I accept the coils. If any of the three change     pitch     then I take the time to address the coils </blockquote></div>