Guitar players use a capo to shift the key on the guitar to match their vocal range. For the non-guitarist it can be confusing to figure out the right key to accompany the song.
This calculator makes it easy. Select any two buttons and it will figure out the third.
Example: The guitarist is fingering the chord of "C", but he has a capo at the fifth fret. Select "Fingered" at "C" and "Capo" at 5 and the calculator shows you the "Actual" key is "F".
Example: The guitarist knows how to play the tune in "G", but your vocal range needs to be in the key of "D". Select "Fingered" at "G" and "Actual" at "D". The calculator tells him to place the capo at fret number 7.