 Di Justo and Gertz compiled a handbook for using Arduino to develop these photometers in 2012.The handbook refers to formula_1 in equations () and (), as the "AOT" (Atmospheric Optical Thickness), and the handbook refers to I0 as the "EC" (extraterrestrial constant).The manual suggests that once a photometer is constructed, the user waits for a clear day with few clouds, no haze and constant humidity.