guide device 12 appears at the top of the exploded view just below the upper cover 22 and contains several preferred elements these include left and right sides steeper than the front and back and of a concave nature particularly in the areas proximal to the fingerprint sensor 16 the front of the finger guide device is concave from the sensor window to the top ridge and has shape derived from a short set of radii to create its generally concave contour the rear section radii create the least steep concave contour and are meant to cup the portion of the finger or digit between the preferred print and the remainder of the digit adjacent to the body the end of the finger guide device furthest from the fingernail contains a continuation of the feedback ridge but is not intended to use the finger joint or skin ridge under the joint as a means for positioning the finger adjacent to the sensor 16 the sides of the finger guide device form a recess that receives the finger of the user accordingly the sides of the finger guide device have the same general shape as the finger in the first preferred embodiment of the finger guide device of the present invention the sides.