Heliographs

The heliograph is an instrument that measures the daily hours of sun (solar radiation) on paper.
It is based on a very simple mechanism, a glass sphere always facing south, through which the sun's rays pass, concentrating on a beam of light, which burns a cardboard or graduated paper located at the bottom. The path or trace of the burned paper marks the hours of sunshine. The most common and homologated heliograph model is the Cambell-Stokes model.