Hi Julia, Do a google search on "relative humidity". Ambient humidity is the level that exists *right now* in the room. R.H. Suppose you have 1 liter of air and it is at 20 degrees Celsius. Suppose the measured humidity inside the container is 30%. If one increases the temperature without allowing any air to escape the humidity will remain at 30%. If on the other hand one allows air to escape--then there are fewer molecules of air--and fewer molecules of water so the "relative" humidity will be lower. Most manufactuers seem to suggest 42% but a few recommend 50% (The old Canadian firm of Heintzman recommended 50%). Wood may crack below 30% R.H. and rust may start at 65% so anything within those limits is "mechanically safe". However I do have data that suggests that even a 5% RH change will cause A4 to drift 4 cents (if the piano is allowed to reach equilbrium). I believe optimal would be any humidity level between 30% and 60% so long as it *never* changed. I.E. 35% 24/7 or 55% 24/7. At 11:30 AM 3/27/2006 EST, you wrote: > Greetings, What is the difference between relatrive humidity >and ambient humidity? Am I even asking the right question? Perhaps I just >want to know what relative humidity means. pianos? Julia >Gottshall Regards, Don Rose, B.Mus., A.M.U.S., A.MUS., R.P.T. Non calor sed umor est qui nobis incommodat mailto:pianotuna at yahoo.com http://us.geocities.com/drpt1948/ 3004 Grant Rd. REGINA, SK, S4S 5G7 306-539-0716 or 1-888-29t-uner
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