Wintact WT1357 Digital Sound Level Meter, Range: 30dB~130dB Features 1. Automatic calibration to ensure accuracy. 2. Automatic linear compensation: this advanced software program improves the accuracy by correcting the nonlinear accuracy of the sensor. 3. Quickly adjust the sound speed thickness and quickly call out the stored data 4. Coupling status indication: observe the coupling icon to see whether the coupling is completed. 5. It has 12 thickness measurement storage and calling functions to facilitate high-altitude operation or field operation. 6. Sound velocity measurement. 7. The sound speed of 12 gears of different materials is adjustable. 8. Thickness alarm setting. 9. LCD backlight display. 10. Low battery indication and automatic shutdown. 11. Metric imperial selection. Specification 1. Accuracy: 1.5dB (under reference conditions) 2. Measuring Level: 30-130dB (A)35-130dB (C) 3. Frequency Range: 31.5Hz to 8.5KHz 4. Linearity Range: 50dB100dB 5. Digital Display: 5 digits 6. Resolution: 0.1dB 7. Bar Graph: 50 dB (scale at 1 dB step for monitoring current sound pressure level display) 8. Overload Indication: OVERUNDER 9. Frequency Weighting: A and C 10. Level Ranges: 30-80dB, 50-100dB, 60-110dB, 80-130dB 11. Self Calibration Time: 3sec 12. Sampling Rate: 20 timesseconds 13. AC Signal Output: 0.707Vrms full bar graph, output impedance is about 600ohm 14. DC Signal Output: 10mVdB,output impedance is about 100ohm 15. Dynamic Characteristic: FAST (high speed)SLOW (low speed) 16. Power Supply: 4x AA 1.5V battery or DC 6V 100mA (not include)