Long description
This drawing shows a string of six thermal resistances each drawn using the convention for electrical resistances, a zigzag line with a horizontal line at each end. The resistance at the left represents the outside surface thermal resistance and is labelled 'R' subscript 'S' 'O'. The next four resistances represent those of different layers of the wall and are labelled ‘R’ subscript ‘1’ to ‘R’ subscript ‘4’. The final resistance at the right represents the inside surface resistance and is labelled 'R' subscript 'S' 'I'.