Ron Guth: Several interesting varieties comprise the 1820 Half Dollars, determined by the base of the 2, whether the 2 ends in a point or a knob, whether the coin is an overdate, and whether the date is small or large. The result is five major varieties in some combination of the preceding, plus quite a few individual die varieties that require closer examination. The subject of this discussion, the 1820 Square 2, Large Date, No Knob, is pretty self-explanatory: the base of the 2 is flat (or squared) instead of curving, the date is Large (requires comparison to determine the correct size), and the top of the 2 ends in a point instead of a knob. In terms of surviving examples, this major variety appears to be the second rarest of the five, though it should be pointed out that the populations of all five are fairly close. Mint State examples of all five varieties are scarce to rare, and the 1820 Square 2, Large Date, No Knob is no exception. As of the April 2012 PCGS Population Report, PCGS had certified only 18 Mint State examples, the finest of which is a single PCGS MS66.