Sound Decibel Meter, GoerTek Digital Mini Sound Pressure Level Meter, Audio Noise Measurement 30-130dBA,MAX/MIN Hold,Auto Backlight Display-3AAA Battery Includedd (GM1352) Measuring Range:30~130dBA ; +/-1.5dB Accuracy with 0.1dB Resolution; Records Max/Min values over time ; Fast Responding . Powered by 3*AAA Battery (Included) .Large LCD screen . Measures in dBA Frequency ; Frequency Response: 31.5Hz~8.5KHz. Auto Power Off or Manual Shut Off by Pressing the Power Button for Two Seconds. There is a calibration knob. You can make use of the calibration function to ensure the accuracy of measuring noise value, reducing error. With a wind-resistant ball, while reducing the effects of wind noise. It is Designed to fit comfortably in the palm of your hand. Auto power-off or manual shutoff by pressing the power button for two seconds. MAX/MIN Hold Function will hold the highest/lowest reading until a higher/lower reading is picked up. Normally you dont need to calibrate it because it was calibrated before delivery. There is a a calibration knob. You can find some tool fit the knob size to poke into the knob. Like needle, small cross screwdriver, iron nail, toothpick and so on.