Thanks for your reply. The trouble is I do not really know what offsets I should tweak. Firstly, did you alter any of the settings for the clouds - which is done by the percentage from the solar.I did not alter any of the settings for the clouds. What I did was tweak the 0% value for a reading of zero about an hour after sunset. I allowed the sensor to cool off after the sun went down. I then tweaked the 100% value on a very clear day, at Celestial Noon for a 100% reading. It will take some time (days) to do this. Also, wait between changing the settings. This will give the program time to update and settle down.
Try setting the maximum thresold (100%) to 13 /1 and the lower (0%) to 1 /1 and see what happens.
Have you noticed any difference (or is it early days) when you have the sun, but little heat from it, as we have in our winters. You can have a really bright sun, but not so much heat, therefore causing an incorrect figure.No.
It appears to me if you want to measure total radiation, the 100% radiation should be measured on a very clear day, at Celestial Noon, on the longest day of the year (summer solstice).