The TPI 510 Solar Irradiance Meter displays results in either W/m2 or BTU to determine the optimal angle of inclination for siting of solar panels to achieve maximum efficiency. Specifications of the TPI 510 Battery: Approx 100 hr Accuracy: typically within +/-10Wm2 [+/-3BTU/(ft2*)] or +/-5%, whichever is greater in sunlight; additional temperature induced error +/-0.38W/m2/°C [+/-0.12BTU/(ft2*h)/°C] from 25°C Operating Temp. & RH: 5°~40°C, below 80% RH Storage Temp. & RH: -10°C~60°C, below 70% RH Display: 3-1/2 digits LCD with maximum reading 1999 Sampling Time: approx 0.25 second Resolution: 0.1W/m2 / 0.1BTU/(ft2*h) Over-input: Display shows “OL” Range: 1999W/m2 / 634BTU/(ft2*h) Dimensions & Weight: 132(L)x60(W)x38(H)mm, approx 150g EMC: this instrument is EMC-compliant and has undergone compatibility tests according to EN61326 (1997) + A1 (1998) + A2 (2001) Don’t forget once you have purchased and received your TPI 510 Solar Irradiance Meter leave a "Customer Review" and share your thoughts with others.