1797 Dimes appear in two major varieties, based on the number of stars on the obverse. One version shows sixteen stars to represent the total number of states then in the Union. The second version shows thirteen stars to represent the thirteen original states (the second version became the accepted norm after Mint officials decided that they would soon run out of room on the coins if they kept adding a star for each new state).
Only a single die variety comprises the entire population of the 1797 16 Stars Dime. In it's earliest state, the die is perfect. In later states a crack begins to develop over the top of the date; this eventually develops into a serious crack that causes the lowest portion of the die to sink and (presumably) break off at some point, rendering the die useless.
A small handful of 1797 16 Stars Dimes exist in Mint State, led by the remarkable, late state example from the Pogue Collection (the MS66 example illustrated above).