OT- In Philosophy there is a paradox called The Ship Of Theseus. Theseus’ ship was preserved by the Athenians for centuries, by replacing planks as they rotted away with new planks. Eventually every single piece of the boat had been replaced, so that even though it had been in continous existence, not one particle of the original material remained. Was it the same ship?

I find myself in a similar paradox with (my Grandfather)Pap’s watch. Major parts of it are completely worn out. It might not be possible, no matter how much of the movement I replace, to get it working properly. OTOH, I have just acquired another movement of the same make and model, made no more than a year later (ca 1904). It’s running beautifully, and has none of the problems of the original movement in Pap’s watch.

If I replace the original movement with this one, is it still Pap’s Watch? If not, how much of the original movement can I replace with parts from the running one, and still have it be Pap’s Watch?