Complex sentence: The diagram of interval qualities above can be used to determine how quality changes as accidentals are added Adding an accidental to the lower note has the equivalent effect on the interval name as adding the opposite accidental to the upper note.
Split into simpler sentences: The diagram of interval qualities above can be used to determine how quality changes as accidentals are added. It was assumed above that adding an accidental to the lower note has the equivalent effect on the interval name as adding the opposite accidental to the upper note.