The pressure gauge and tread tester comes with a valve to let out the air if required the pressure gauge has 2 leds for improved illumination of the tester measuring area psi bar kpa kgcm tyre tread tester 0 10 mm red led no tread yellow led not enough tread green led tread ok the device has magnets on the rear and a valve to let the air out it comes with an easy to read illuminated lc display 2 x aa batteries and abs casing