The genuine 3536 is approx. 38mm diamter minus the crown, approx. 42mm with the crown. The rep measures the same.
Take a look at this auction link: http://www.ebay.com.my/viItem?ItemId=290123190224
Compared to the SD, the 3536 appears to be bigger. In fact, the 3536 is strange: overall it looks much bigger than it is. But it is in no way as heavy, large or thick as the mighty Ingenieur.
Here are some quick pics compared to my genuine 5513, which is about the same size as the SD (but not as thick as the SD).
Overall, like I said, it is nowhere near as big as the Ingeniuer. It is sized more like a 40mm Submariner. I would go out and buy the real thing right now if it was sized as big as the Ingeniuer. But since it is not, a rep is fine for me.
Hope this post helps.
Cheers from your buddy Euno