15% of the reverse is struck, and none of the obverse. The error occurred when the press was striking coins with insufficient striking pressure, and then this coin was fed into the striking chamber and had an off-center planchet lying on top of it. It was struck with an incredibly weak strike, resulting in the off-center planchet's pushing downwards into the coin's central planchet area and allowing a strike of occur in that area of the reverse. The obverse only shows a "rim impression", which is from the planchet which was struck into it on the obverse. Neat coin and rare like this.