I am still very new to learning guitar (specifically, Classical fingerstyle). While this is the first time I am doing this "seriously", I HAVE tried to learn guitar before, just very badly (and usually with crappy instruments that have been handed down and mistreated by family). I am currently using a tuner app on my phone, although I just ordered a nicer clip-on tuner (Snark SN-2). In the past I've used other mic'd chromatic tuners.
I'm just curious why it is, when tuning, that when you get a note "perfect" it's only exactly in tune for a moment after the string is struck. After that moment, the tuner starts to frequency wobbling sharp and flat around the ideal tuning.
What causes that to happen? I've read a bit about tuning now trying to find out, and everyone just seems to repeat that it's the note played originally that has to be as close to exactly in tune as possible, and not to worry about afterwards.
What confuses me is that the string length never changes, so the wavelength shouldn't change. The frequency may slow down as the string stops vibrating as fast... but why would it sometimes go up too? Maybe I'm thinking about it wrong?
Wouldn't this affect sustained long notes, or is it mostly imperceivable by the ear?