Digital smart level measures angles in 360 degree range with angle accuracy to 1/10 of a degree. Mode button lets you see angles in 3 ways: degrees, % of slope or pitch. Audible tone alerts you when tool reaches level or plumb. Hold button freezes angle measurement on display for easy conversion reading from one mode to another. Resets to factory accuracy with a touch of a button. Module is encased in high impact resistant ABS polymer case, sealed against dirt or water penetration. Fits into any standard rail. Automatic shut-off after 5 minutes. Uses 9 volt battery (not included). RAIL: Heavy gauge aluminum high impact resistant vials and covers for durability, can be adjusted, American 6000 brand series. Is similar to carpentry & construction magnetic levels but without the magnetic edge. Heaviest gauge I-beam. Impact resistant vials and vial covers for durability and long life. End caps help protect tool against drops and shocks. Fixed vials are hand set to working edge. Ideal for the carpenter.