This unique tool allows thickness measurements of stringed instruments to be made without disassembly. The small counter-magnet is passed through the instruments f-hole and follows the gauge around every edge and curve, allowing the exact thickness to be measured at any place on the body. Accurate to within 0.1 mm, calibrated for making measurements while holding the gauge in a vertical position. Quick and easy to use, with no risk of damaging even the most sensitive varnishes. Ideal for the study of old instruments, locating old crack repairs, making sound adjustments, etc. Comes in a protective case. Magnets with rounded surfaces for high precision spot measurements also on concave surfaces. Measuring range 3-12 mm, 2 magnets. Ideal for Cello, Bass, Archtop Guitar, Bass Viol and other uses such as Bowl Making.