I've had my Fortis B-42 Pilot Pro Chronograph GMT (V7750 movement) for 10 days; it was used and about 2 years old when I bought it, though it had been sitting in a cabinet in the dealer's workshop for at least 6 months previously. This is the first automatic watch I've bought in about 26 years, having had quartz chronographs and watches since 1983. My only other auto was a Seiko 6309 Diver, which was never serviced in 27 years but which ran consistently -30 secs/day.
I've checked the Fortis against the telephone speaking clock every few days and for the first couple of days, I was stunned by its accuracy - about -1 sec day. After 1 day it was 1 sec slow; 3 days -4 secs; 6 days -10 secs; 9 days -20 secs; 10 days -23 secs.
Now 2.3 secs/day is pretty good, but the rate seems to be increasing by about 0.2 to 0.3 secs per day and at this rate [of change of rate, if you see what I mean] it might get to -12 secs /day in another month.
I don't take the watch off, except, usually, to shower, so it's consistently wound. It's not had a bang, so I can see no reason why the rate should change.
Is this normal? How far should I expect the rate to drift before I take it back and ask the dealer to adjust it?