Each number field has a unique label of the form d.r.D.i where

- \(d\) is the degree;
- \(r\) is the real signature; the full signature is therefore \([r,(d-r)/2]\);
- \(D\) is the absolute value of the discriminant;
- \(i\) is the index, counting from 1. This is in case there is more than one field with the same signature and absolute value of the discriminant: for example 4.0.1008.1 and 4.0.1008.2.