<html> Hi Terry,                A few questions,   1. What time period are we talking about for noticeable tuning drift?   Does the tuning drift always go flat, or is seem unpredictable in different registers?    Some Yamaha models tend to go a little sharper than average, at the end of the long bridge, with high humidity swings, yet the bass strings are much more stable.  The octaves across the tenor break will  become noticeably wild.  This can be a clue to nothing being amiss structurally.  Before installing Damp chasers, some of out University studios have a C3 and G2 in them.   It was a constant problem trying to keep them together. After installation complains stopped.      Just a thought for you. Regards Roger t 07:24 AM 9/23/02 -0400, you wrote: <blockquote type=cite class=cite cite>I agree that you state logic, but the stable microgrand is actually more in the direct path of the AC vent. The Yamaha does not get blown on. The pianos are in her separate studio. It is a former in-law type house. No cooking is done in there, nor are showers taken, so humidity is presumably fairly stable, just varying with outside general directions. As I stated, she will purchase a cheap hygrometer and start monitoring RH. No windows near the Yamaha. The microgrand is next to sliding glass doors that are never opened. No plants in house. No holes in wall. All these factors raise my concerns regarding some type of structural condition. Terry Farrell</blockquote> </html>