Beginning with the 1880 census, the censuses are indexed by the Soundex system.
The Soundex is a coded surname (last name) index based on the way a surname sounds rather than the way it is spelled.
Surnames that sound the same, but are spelled differently, like SMITH and SMYTH, have the same code and are filed together.
The Soundex Coding system was developed so that you can find a surname even though it may have been recorded under various spellings.
To search for a particular surname, you must first work out its code.
This program help you do that: just enter the surname, and out comes the code.