The thermometer does not have a watch movement, but rather a horseshoe-shaped constellation of steel and brass. When the temperature rises, the shape of the horseshoe changes, thus making the hand move. The pocket thermometer, made in this shape in 1801, was one of Urban Jürgensen's most important inventions and was made in close collaboration with his father-in-law Houriet. The can be found with various different dial signatures, including “Larpent & Jürgensen”, “Urban Jürgensen” and “Louis Urban Jürgensen”. Similar pocket thermometers can be found in John Knudsen's book “The Jürgensen Dynasty” on pages 52, 92 and 129.