The invention helps build a practical telescopic gauge to measure length and end angles needed for sound post in stringed instrument. It shows improvements of telescopic type gauge where, first adding a spring to control force while extending or reducing length and second adding rounded members at least one end of the gauge overcome difficulties in measuring the length. Further a three part swivel end consisting of ball, swivel cap and resolution plate held together by magnetic force allow satisfactory angle measurement. Because magnetic force is used, the swivel end parts can be removed leaving rounded ball end open for length measurements, then other components are added as required. This type of swivel end is also useful in improving currently available caliper type gauge.