The Soundex/Miracode is an alphanumeric coding system designed to keep together the names that sound similar regardless of their spelling. Only certain key letters are used. Vowels are ignored. The result is a letter followed by exactly three digits.

Soundex codes are used to help index the persons found on the federal census records. The 1880 census was the first to have Soundex codes applied.

To determine the soundex code for a given surname, use the following rules:

1. write down the first letter of the surname
2. all letters following the first letter must be coded into a three-digit number using their soundex codes. As soon as three digits are gotten, all remaining letters are ignored.
3. all double letters (e.g. the letter 'l' in William) are coded as a single letter
4. if the initial letter and the second letter have the same code then ignore the second letter
5. if two different consecutive letters have the same code then the second letter is ignored
6. if all of the letters are used up but the three digits have not been determined then use zero for the remaining digits
7. surname prefixes should be ignored. These include: D', De, de, dela, della, Di, Du, La, Le, Van, Von

Soundex is not perfect. Consider the following:

• names starting with 'Ph' and 'F' sound alike such as: Phillips and Franklin
• names spelled differently in other countries that become 'Americanized' such as: Tshantz became Shantz
• names beginning with 'Ei' sound like just 'I' such as: Eisenhower and Ireland
• names with 'gh' followed by 'ou' make the 'gh' sould like the letter 'f' such as: Rough
• names with the letter 'l' proceeded by 'ou' and maybe some letter after it often make the letter 'l' silent event though the letter 'l' gets coded such as: Would, Could, Gould