<html> At 03:35 PM 4/10/2004 -0400, you wrote: <blockquote type=cite class=cite cite>In a message dated 4/10/2004 2:00:24 PM Central Standard Time, pianotuna@accesscomm.ca writes: <dl> <dd>Hi Wim, <dd>Possibly you are pounding too hard. Very small changes in humidity cause <dd>pitch instability in unisons. I've documented that on the ptg list. I wish <dd>I had better tools to analyse what is going on. Temperature (stage lights) <dd>as I'm sure you know can make huge differences very very rapidly. </dl>I know stage lights can make a difference, but those differences are by way of the soundboard. </blockquote> Stage lights affect the strings, (and to a lesser degree, the plate), not the soundboard. Humidity affects the soundboard. <blockquote type=cite class=cite cite>If the humidity causes pitch instability, why just one one string? Why not in all of them? </blockquote> The amount of non-speaking length between tuning pin and nearest pressure point is strongly related to "which" strings are affected. Depending on "what" is doing the affecting, so-to-speak, methinks. <blockquote type=cite class=cite cite>Why do some strings go up, and other go down?</blockquote> Over-pounding will make strings go sharp, later. Sometimes much later, like... after some chords and pedaling have taken place. For performance pianos, I always do a series of four-note chords with both hands and lots of pedal. Brings out the weak pin technique quickly. Check, double check, and then.... check again. It's the only way I can keep from being embarrassed. Even then.... <blockquote type=cite class=cite cite>  Wim </blockquote> Later, Guy</html>