Once re-strung, the adjustments begin: Levelling the unisons is vital for hammer strike and damper seating. Using a stringing hook, each string is lifted enough to correct the residual string wire curvature, releasing the pressure towards its agraffe.
A metal block of some kind (here I’m using the brass capstan from a lyre rod) suffices as a levelling guide:
As you might expect, this adjustment is not permanent, but does become increasingly accurate and stable when repeated over the first 2 years of a string’s life.
(Piano wire seems to continue stretching – ever more slowly, of course – for about 2 years. After this time, it becomes amazingly stable – but then also begins its slow deterioration, with gradual loss of tonal colour. This decline lasts maybe 10-30 years, depending on how much/hard the strings are played and how the piano is stored.)