Lutron SL-4022 Sound Level Meter. Frequency weighting and time weighting are meet IEC 61672 Class 1. Large LCD display, easy to read. A & C weighting networks are conformity to standards. FAST & SLOW dynamic characteristic modes. AC output for system expansion. Build in adj. VR, available for easy calibration. Condenser microphone for high accuracy & long-term stability. Build max. hold reset switch. Max. Hold function for stored the maximum value on display. Warning indicator for over and under load. LCD display for low power consumption & clear read-out even in bright ambient light condition. Used the durable, long-lasting components, including a strong, light weight ABS-plastic housing case. Compact and heavy duty housing case. Low battery indicator.