On the vintage Astronaut the time was set by a recessed key on the case back which would be flipped up and twisted leaving no trace of a crown on the watch's profile
link from any angle. Here Accutron recessed the crown
link into the side of the case so it tucks under the bezel to keep the aesthetic when viewed from the front and the half sapphire case back mimics
link the shape of that original key while leaving space for the engravings for which of the 300 watches you have.