1820 Bust Half Dollar in Extra Fine 40 Details Scratched condition as graded by ANACS.  O-104 is on the label.  It is most probably an O-104a.  This coin has nice toning & surfaces, there is a hairline scratch in the obverse right upper field & some light scratches on the reverse lower right edges that are noticed under magnification.  This is the rare Large Date, Square Base, Knob on top of "2" which is a R-4+ for variety.  The very late die state for this reverse die which has two known major die cracks & is present & distinct on this coin as well as a third die crack.  The 1st crack runs from 4:30 to 6:30 the second one which is distinct for this variety & runs from 2:30 between the edge at the R & I into the right edge of the lower part of the Eagle's wing, the die crack extends on this coin below the Eagle's wing into & beyond & below the Eagle's right claw.  On the mid-upper part of this die crack it looks as if the die is starting to buckle on the right side of the crack.  There is also another die crack running from the lower part of the left side of the first die crack described & starts at 6:30 as well in the other direction.  This crack runs through devices & fields along the left side of the reverse to the top left of the reverse & under heavy magnification parts of it can be noticed running close to the edge along the right side as well.   The reverse edges are also rounded into the field & not distinct due to the worn die state as well.  The O-104a which this coin probably is, is very rare & therefore a R-7 with only 4 - 12 survivors for this sub-variety of this rare variety.  The reverse die on this coin since in a very late die state was not probably going to last much longer & crumble apart due to all the cracks.  This was probably one of the last strikes that this die combination could be used for to make this variety.  A very attractive rare & interesting coin.