1. and 2. Obtain measurements of your instrument's fretboard radius using the bottom radius of the gauge 3. Then use the matching top radius of this gauge to determine the proper height adjustment for saddles. 4. These come in the most fingerboard radius and easy to measure the radius from either above or the strings. 5. Use these to accurately setup your guitar bridge saddles to match the fingerboard radius. ruler side:Could be used for gut guitars, electric guitars (raise or lower string height), acoustic guitars,and guitars (including six string guitars) to adjust space.this tool set is suitable for measuring all kinds of electric & acoustic guitar, electric , electric box guitar fretboard that measured in radians to adjust the strings piano code. Usage: these guitar luthier tools are good gifts to guitar technicians and guitarists to maintain and repair their instrument themselves in a short time, reducing buzzing; Good tools for electric guitar, acoustic guitar, , and folk guitar, etc. 9: 7.25inch 9.5inch 10inch 12inch 14inch 15inch 16inch 17inch 20inch Colour: Silver Material: Stainless Steel Package Contents: 9 x T- rulers 1 x string height ruler Only the above package content, other are not included. Note: Light reflection and different displays may cause the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.