This paper introduces the Magpick, an augmented pick for electric guitar that uses electromagnetic induction to sense the motion of the pick with respect to the permanent magnets in the guitar pickup. The Magpick provides the guitarist with nuanced control of the sound which coexists with traditional plucking-hand technique. The paper presents three ways that the signal from the pick can modulate the guitar sound, followed by a case study of its use in which 11 guitarists tested the Magpick for five days and composed a piece with it. Reflecting on their comments and experiences, we outline the innovative features of this technology from the point of view of performance practice. In particular, compared to other augmentations, the high temporal resolution, low latency, and large dynamic range of the Magpick support a highly nuanced control over the sound. Our discussion highlights the utility of having the locus of augmentation coincide with the locus of interaction.