How to :Just press the button on the front of the device. the sensor window on the top panel of the meter directly at the UV source. Read the notes on the LCD screen and make notes as needed. To get more data, run multiple tests at the distance and average. Battery operating voltage is 3V to 2.5V. Below 2.5V the LCD number will begin to darken, indicating the need for battery replacement.Item Type: UVA MeterIrradiance Range: 0-1999 W/cm UVAResponse: p=320-400 nmResolution: 1 W/cmConversion Rate: 3.0 Readings / SecDisplay: 3.5-bit LCDSize: 0.4 Inches HighOperating Temperature: 32Fahrenheit to 90FahrenheitOperating Humidity: 5% to 80% RHAccuracy: +10% REF NISTProduct Size: Approx. 165 x 75 x 30mm / 6.5 x 3 x 1.2in Supply: 2x1 5V AA Battery (Shipped Without Battery)Lens: UV GlassWeight: Approx. 231g / 0.5ozColour:As shownMaterial:Silicone+ABSPackage Contents:1 x UVA Meter1 x English manualOnly the above package content, other products are not included.Note: Light and different displays may the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.