$4.99 from Artsiness
Circle Theory is a Circle Of Fifths (sometimes known as a Circle Of Fourths). The Circle Of Fifths is a tool for musicians to assist them in seeing the relationship between notes, provide key signatures for both major and minor scales, assists in transposing between keys, and it also has a helpful guide to figure out note intervals per musical mode.
• Tap or drag on the outer ring to change the tonic note / key signature
• Double-tap the outer ring to cycle through the inner ring displays
• Double-tap the center of the circle to cycle through the clefs
• When the inner ring is displaying a musical mode, drag the inner ring to select a new mode
• When the inner ring is displaying the transposition assistant, drag the inner ring to select a new starting key / note