I don't want to mislead anyone, the difference appears to be a variation rather than anything really significant. The new AQ4000-51 series don't have the power reserve dial but have an A060 movement rather than the A010 used in all the other Eco-drive models. I notice that there is way for the wearer to ascertain the power reserve but I can't see anything on the photos provided by Mr Citizen. I like the idea of not having a fuel gauge but I don't like not having lume and I'd like to know the the diameter. The specs say "white plating" rather than the usual Duratect but that may merely be translation rather than an actual change.