Miszna do Kapłańska 13:39

Rabbi Shimon said: when is this the case? When the quick flesh was exactly the size of a lentil. But if it was larger than a lentil, the excess is a sign of spreading of the inner one, and the outer one is unclean. If there was white scurf less that the size of a lentil, it is a sign of the spreading of the inner bright spot but it is not a sign of spreading of the outer one.