I typically set my watch to the second vs iphone clock (yeah, lol....) and then I checked every day once a while to see if it is still matching.
My experience with what I own is Rolex, Omega and Patek are very accurate (+/-2 s) followed by Lange (+/- 4s).
Chopard as you mentioned is not that accurate even it is COSC, but I guess 6sec is within the specs. This AE was ~8sec behind each day and I'm not too concerned as long as it's working within my tolerance but not 1min in 10min.
Thanks for your answer and info.