Having now owned this watch for a few weeks I am amazed by its accuracy. I only own two mechanical watches the new Portofino (my previous Portofino was stolen)and a seven year old Omega Seamaster chronometer 1120 calibre,(model now unavailable) I really like them both. I alternate daily between the two and whilst the Omega gains slightly about 1 second a day the Portofino has stayed spot on, amazing! My theory is wearing them this way, whatever gain is made in a day is lost on the day it's not worn so keeping accurate time without the need to adjust them. On the day a watch is not worn it is critical to store it in the optimum position, with mine face up for the Portofino, crown up for the Omega,(a certain amount of trial and error required here). I have to say my original Portofino was just about as accurate that's why I bought another, I hope the thief that stole it appreciates it as much as I did. Well done IWC for producing such fine timepieces.