I have one of the early 29As, and I find that it gains a few seconds a day if wound every 24 hrs. More than acceptable of course, but if I leave it until the last few hours of its 40 hour power reserve it will start to lose time, so in practice I can keep it very accurate indefinitely by carefully managing the frequency at which I wind it. Which is very easy to do; I wait until it's 5-10 seconds slow, then wind it fully again.