I just checked a Yamaha P32D while it was cold and it averaged 14 cents sharp. After playing it for 3 minutes to literately warm it up, it now averaged 7 cents sharp. Metal expands and contracts. I am thinking it’s temperature, more than moisture, that is changing the metal reeds density. A warm humid room would be recommend.
From an accordion website:
“The colder the temperature, the more sharp the pitch, as the cold reeds are stiffer and vibrate faster than warm reeds.”
