Use your basic Movable Do Disc with the Absolute Pitch Attachment combined with the larger APA to transpose written melodies or chord progressions to a different key. Although there is plenty of music notation software available that can do the job, writing scores for transposing instruments and transposing songs to your or someone else’s comfortable key are skills that come in very handy and make you a very complete musician.
In this example, the inner APA shows G=do, while the outer APA shows Bb=do. If I would transpose a piece of music written in staff notation, or a chord progression written in chord symbols from G to Bb, this set-up immediately shows me what to write down.
In G major we might have the chord progression G C D G. Transposing this to Bb major would give Bb Eb F Bb. It is the same progression, in a different key. The goal of course is to gain such an understanding of tone relations and of all the keys that these steps can happen in your mind instantly!