The weird date wheel with holes to lighten rotating mass!
Yeah they are pretty cool actually, they have a neat system going on there.
If you look at the "24" area on the dwo, youll see a tiny tab, which is bent down.
The factory datewheel, with the ETA datewindow location, sits below and has a notch in it to recieve this tab.
The center if this DWO sits on the original DAYwheel post and is secured with a tiny c-clip, so its easily removed, and when replaced, because of the tab, PERFECT alignment every time. no glue neccessary for this setup.