To add to this, what size is the frame? Some builders have been known to flip the seat tube on larger frames so the BB end is 27.2 and post end is 26.8 etc...
It is a 53/54. I think it is one owner from new, I bought it from a mature gent so surprising for him to have inserted the wrong size post, but you never know.
Sorry for bombardment of posts.
Maybe post a pic of the whole frame, see if anyone recognises the model and can confirm the diameter.
Sheldon only has two Ciocc models listed - both 27.2:
Ciöcc Designer 1984 27.2 Columbus SL
Ciöcc Mockba '80 1984 27.2
https://www.sheldonbrown.com/seatpost-sizes.html