My sky unit uv reading seem to be much lower than nearby units. It is a clear cloudless day in the central valley of California, upper 80’s, but uv reading is only 4.7. Sky units 30 miles north in the same hot valley show 8.0, similar to other relatively nearby units. My sky is mounted on a 10 ft pole attached to the chimney of a 2 story house, so no interference by tree shade. They have consistently been low since it was installed
Any ideas?