HARMONICSENSE  Music is not exact science, and a lot is open to interpretation. Many music theorists have the view that chords are composed out of thirds stacked on top of each other, which would lead to variations on 1,3, 5, 7, 9, 11, 13. The 13th scale degree sounds the same as the 6th, so many people just replace the 13th with the 6th.

That being said, we updated the formulas to include (6) next to 13 to avoid confusion for some people.  
(Version 1.4.1)

HARMONICSENSE  Thank you for your comment. We have ChordMate Express which costs $20. It's a lot more than a database of chords because it allows you to try how chords fit together in a chord progression. The chord progression can be saved (there is an option in the Chord Progression menu). Aso, diagram export and support of custom chord diagrams make it a great tool for creating beautiful songsheets, lessons, etc.

The Pro version supports alternate tunings. We don't use a database for storing chords, so every tuning is supported equally well. Another big feature of the Pro version is support for altered chords. Any chord degree can be altered in any chord, which is much more powerful and flexible than a chord database.

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The Harmonic Sense Team.  
(Version 1.4)