It can be helpful to simplify the accidentals when analyzing an interval.

If both notes have the same type of accidentals, the quality of the interval is the same as the quality of the interval without accidentals:

In the previous example, all seconds are major. It's easier to analyze the first one without accidentals.

If one of the notes is double-sharp and the other is sharp, make the sharp note natural and the double-sharp note sharp. The quality of the interval remains the same:

In the previous example, both fifths are augmented.

If one of the notes is double-flat and the other is flat, make the flat note natural and the double-flat note flat. The quality of the interval remains the same:

Both fourths in the previous example are augmented.

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