A computer-guided system for determining the disposition of an object, the computer-guided system comprising:a platforma compass removably and adjustably mounted to the platform, the compass comprising: a first arm having a proximal end and a distal enda second arm having a proximal end and a distal endthe proximal end of the first arm being removably and adjustably mounted to the platform by a magnetic ball mount, wherein the magnetic ball mount comprises a spherical encoderthe proximal end of the second arm being movably mounted to the distal end of the first arm by a pivot mount, wherein the pivot mount comprises an angular sensor anddetermining means for determining the disposition of the distal end of the second arm relative to the platform by using data from the spherical encoder and the angular sensor.
