 This leads to thirds quite close to pure (compared to equal temperament) in the 'home' keys of F, C and G major and in D, A, E and B minor.1/6 comma extended meantone intonation (the 55-comma system) was the standard intonation ideal in the 18th century.On the other hand, there were very impure Pythagorean thirds in the remote keys of B, F# and C# major and in G#, Eb, Bb and F minor.