Task: Question Answering
Input (English): Context: From Today in Science History : Anna Botsford Comstock ( Died 24 Aug 1930 ; born 1 Sep 1854 ) . ( nee Anna Botsford ) American illustrator , writer , and educator remembered for her work in nature study . Pliny the Elder ( Died 24 Aug 79 A.D. ; born 23 A.D. ) . Roman savant and author of the celebrated Natural History , in 37 volumes an encyclopaedic work of very uneven accuracy that was nonetheless an authority on scientific matters up to the Middle Ages . He prepared this as a digest of two thousand ancient books written by nearly five hundred writers . 
Question: What does the speaker mean when they refer to the book as having ' uneven accuracy ' ?
Output (English): The book is n't always consistent with how accurate it is.