This is at LEAST 60% off center, probably more like 65-70%. I certainly hope this was just a clerical error as there is no way it is the percentage listed. (Currently up for auction on GC.)
There is a way to determine the exact percentage, but the math gets ugly. I saw it once in the Chemical Rubber Company manual.
I was told by a former ANACS authenticator that they put a % on a label (let's say 30%) and the customer became irate and said the label should more correctly read 35%! This was at least ten years ago. The grader told me that right then and there ANACS stopped using the %. So, someone should call ANACS and ask if they use the percent any more. If not, this is an older slab.
Okay, but why put the clock number on? We can ALL see that! Have they hired Captain Obvious over there?
Would this be a double error coin? First by the mint, then by ANACS. I have wondered how they calculate percent off center. My usual calculation is to measure the distance from the opposite edge on the unstruck planchet to the "edge" of the struck part, or rather, where the rim should have been. (This would be the same distance as from the center of the planchet to the center of the design.) Then divide that number by the with of the planchet. Using the OP's picture I come up with a hair over 66% off-center. By this method a blank planchet could be considered "100% off-center."
If you think about it, the math for off-center strike percentages is disturbingly like the math for partial eclipse percentage calculations. Two things of similar diameter offset to each other?
I would think percent off center and percent covered are two entirely different concepts. In an eclipse, the matter of concern is what area of the sun is obscured vs. the area visible. In percent off center, I would think the matter of concern is how much the center (or edge) has been displaced. The two concepts yield vastly different numbers. Fifty percent displacement of the center will leave far more than fifty percent of the planchet blank, although I don't have the math to say exactly how much.
Wow. I never even CONSIDERED it wasn’t strictly an area ratio problem. Linear displacement? Never even considered it.
Did some googling, and this link appears to show the necessary math, with a graph at the very bottom that shows distance between the centers and resulting overlapping area. http://jwilson.coe.uga.edu/EMAT6680Su12/Carreras/EMAT6690/Essay2/essay2.html
I saw that site and concluded it was far more work than I wanted to give it, especially since I don't think the percent off center should be measured by the overlapping area. Perhaps ANACS did that and concluded the overlapping area was about 25% of the total.