Most 1834 Dimes have a Large 4 in the date, but one die combination has a Small 4. The difference between the two is fairly obvious, especially when the openings in the 4 are compared. However, it helps to have images of the two varieties (or the actual coins) in order to make a positive identification.
The Small 4 variety is approximately 1.5 times as rare as the Large 4. The PCGS CoinFacts Condition Census for the 1834 Small 4 Dime consists entirely of Mint State examples, starting at MS64 and going all the way up to MS67. This variety also comes in Proof format.