In 1838, 13 stars were added to the obverse of the Dime. Each star was hand-punched into the die, thus the spacing and the placement of the stars is not uniform on individual varieties. Intentional or not, one variety was created using star punches normally used on Half Dimes. Appropriately named the "Small Stars" variety, this one can be "eyeballed" because the stars are smaller and more widely spaced than on the "Large Stars" varieties. Also, the "Small Stars" variety is often found with a die crack connecting the stars on the left. The "Small Stars" variety is roughly seven times rarer than the "Large Stars" variety.
Sources and/or recommended reading:
"Walter Breen's Complete Encyclopedia of U.S. and Colonial Coins" by Walter Breen