Hello Jim, Bellani pyranometer does not record absoulte values of Radiation, it has to be calibrated against a direct recording solarimeter. In most cases , this calibration would have been done already and the values what you get is global solar radiation.So absolutely there is no difference between bellani and high cost pyranometer How ever you need to confirm with the source whether they have done this calibration. sincerely, Ramkrishnan.P.B. Department of Crop and soil sciences Michigan state university Michigan-48823-1325 _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. Share information about yourself, create your own public profile at http://profiles.msn.com.