How do you know if your piano tuner has done a good job?  Sit down and play some heavy handed (fff) pieces for 20-30 minutes after he leaves.  If the piano stays in tune, then he’s done a good job.

After that, it’s all up to temperature and humidity fluctuations.  That’s why pianos are tuned right before a concert and not several days before – you never know what fluctuations will occur in the concert hall.

I had to have my piano tuned three times in 2014 due to temperature and humidity fluctuations.  In October, 2013 we replaced our furnace and right about the same time our dehumidifier bit the dust.  With the new furnace we thought the humidity problems had been taken care of but that was not the case!

An interesting note–my tuner told me if a piano goes “sharp” your humidity is too high.  If a piano goes “flat” the humidity is too low.

Always try to keep instruments made of wood in a fairly consistent environment (heat & humidity), otherwise you risk structural defects and an instrument constantly in need of adjustment.