Features: This meter is an accuracy instrument measuring the strength of sunlight. There are two units that can be selected: W/m² and Btu. It supports maximum value hold function and data hold function. Measure directly without adjustment, steadily measure for a long period. Widely used for solar radiation measurement, solar energy research, meteorology, agriculture, physical and optical experiments. It can also be used to measure the light transmission strength of glass to verify the performance of the glass, for example, car window performance test. Specification: Model: SM206 Resolution: 0.1W/m², 0.1Btu/(ft²-h) Range Error: ± (10%R+2dgts)R: readings Temperature Error: ±0.38W/m²/℃[±0.12Btu/(ft²-h)/℃] deviation at 25°C Display: 4-1/2 LCD display, maximum display numerical value 19999 Overload Display: "OL" Shift: <±1.5% /year Measurement Range: 0.1-1999.9W/m², 0.1-1999.9Btu/(ft²-h) Sampling Time: 2.5 seconds/time Operating Temperature and Humidity: 0~40℃, <80%RH Storage Temperature and Humidity: -10~50℃, <70%RH Battery: 9V battery ( NOT included ) Size: Approx. 132 x 60 x 38mm / 5.2 x 2.4 x 1.5in Weight: 325g / 11.5oz (approx.) .