The only way you can get .001 cent accuracy is with a strobe tuner. It is, however, what is known in engineering as "spurious accuracy" as far as everyday guitar tuning is concerned, and although I would agree that such accuracy would be necessary for piano tuning, most piano tuners do not use electronic tuners.

The big advantage of a strobe tuner like the Campbell is the accuracy it brings to the process of compensating the saddle (and the nut) accurately. Guitars which do not have an accurately compensated nut and saddle (as in the Buzz Feiten system) , cannot play in tune, period. Maybe nobody complains, but they still don't play in tune.

Murray